sounds really messy. So are there much hard feelings between EO and RC over these ECC's? Or is it mostly water under the bridge...
A question to which there is no single answer and no easy answers. And, what follows is a bare-bones overview of the subject.
Understandably, the Eastern Orthodox Churches (particularly those of the Slav Traditions) have historically taken a dim view of the events in their native countries that led to the creation of their Eastern Catholic counterparts - events that sometimes went beyond mere political or ecclesiastical decision-making and proceeded to involve physical violence, destruction of temples, etc. And, in instances where those who embraced Eastern Catholicism deemed themselves to have done so of their own volition - and suffered similar consequences - the same dim view was taken in the opposite direction. How it has played out centuries later sometimes differs significantly from country to country and Church to Church.
In the diaspora of the late 19th century and into the early 20th century, there are curious and sometimes conflicting tales to be told. In the earliest years, one can read in various parish histories of communities comprised of mixed congregations, amicably worshipping under the service of whichever priest happened to be available - with the parish eventually dividing once another priest of the opposite Church or the 'other' nationality arrived on the scene.
Real differences arose shortly, however, when Eastern Catholics began to suffer the loss of their traditions and significant disrespect toward both those traditions and even their presbyters on the part of the largely Irish and German Latin hierarchy. The latter were appalled by the idea of married clergy and it went downhill from there. The battles that ensued played out over a period of 3 decades and changed the ecclesiastical landscape of Eastern Christianity in this country. Thousands of Eastern Catholics returned to the Orthodoxy of their forefathers. Although the Russian and Ukrainian Orthodox Churches each had a presence in the US prior to these happenings, their numbers were bolstered incredibly by these changes and ACROD itself came into existence as a consequence of them.
Small towns and cities, particularly in the Coal, Steel, and Rust Belts were (and are) dotted with competing temples on opposite corners of the same city block. As I'm certain that my friends and brothers, podkarpatska and username, can both testify, these events sometimes resulted in familial splits that continued for generations, with siblings not crossing one another's thresholds or speaking one another's names.
In modern times, in the diaspora at least (though one could not necessarily tell by the interactions on internet fora), much such hostility has mellowed. Certainly, this is true in the relationships between the Byzantine Ruthenians and their brothers and sisters of the ACROD Metropolia, due in very large part to the healing efforts of Metropolitan Nicholas (ACROD), and Metropolitans Judson and Basil (both of the BCA), all of blessed memory. In the homelands, change has been much slower as both the EO and EC Churches are still in recovery from the decades of oppression, persecution, and martyrdom visited on them by Communist rule. The competition for temples that have been bandied back and forth between the two for centuries has effectively recreated the hostile atmosphere of centuries past (forgetting that they just got out from under equal-opportunity suppression). But, even in those nations, relations can't be described as the same across the board. The Carpatho-Rusyns in Europe, both Orthodox and Catholic, appear to have a decidedly more accepting relationship with one another than is the case between ECs and EOs in surrounding countries. The Ukrainian Orthodox in the diaspora also have a notably close relationship with their Catholic counterparts; it's harder to measure that situation in Ukraine as a consequence of the diverse and competing Orthodox Churches there.
With all that said, the Antiochian Orthodox Church and its Melkite Catholic counterpart have historically maintained a compatible relationship, although it's not as close in this country as it once was. The reasons for that are often attributed, rightly or wrongly, to the influx into the Antiochian Archdiocese of large numbers of converts from Protestantism - changing the ethnic dynamic that formerly united the two. The lack of historical hostility between these two entities though is attributable in large measure to the fact that the Melkite union with Rome was essentially a self-driven move, and not seen as coerced. Certainly, in the earliest (18th century) years of that union, there were elements of hostility, but those were comparatively short-lived. In the Middle East, relations between the two are extremely close. As the Melkite Patriarch Maximos V, of blessed memory, once told me, the survival of Christianity in that region transcends inter-ecclesial rivalry in a way that few outside the five who hold the patriarchal title of Antioch can understand.
Among the Oriental Orthodox, relations with their Catholic counterparts have historically been on a pretty even keel. The Armenians and Syriacs, particularly, have close ties with both Rome and the corresponding Oriental Catholic Churches. Relations with the Copts have varied - ranging from close to distant and presently somewhere in between. The Ethiopians and Eritreans are probably the most distant in that regard among the OO. The Syro-Malankara Churches have a benignly amicable existence by all appearances.
The Assyrian Church and its Chaldean Catholic counterpart also have a fairly close relationship, albeit the much publicized decision a few years ago by an Assyrian hierarch to seek union with Rome (bringing a couple of parishes and some clergy with him) troubled those waters somewhat.
Addendum: In looking back at what you asked and what I answered, I suppose that I really spoke more to the rekationships between the EOs and the corresponding ECs and the OOs and corresponding OCs, rather than between Orthodoxy and the Church of Rome (except for what I said about the OOs - the relationships between those and Rome is pretty much the same as between them and the OCs).
In short, I guess I'd say that the EOs pretty much do not want to deal with Rome over the issue of the ECs - looking at the latter either as persons who should return to their Orthodox heritage or as Catholics whose liturgical praxis mimics that of Orthodoxy but lacks the spirit or truth of it. The Orthodox have never completely forgotten that the original concept envisioned and espoused by Rome (now, blessedly, abandoned) in 'allowing' the ECs and OCs to continue their liturgical praxis, etc, was as a way to lure the Orthodox into union by providing a familiar venue. It took a long, long time for Rome to ever see the EC and OC Churches as having a distinct and independent right to exist within the Catholic Communion, rather than existing for that purpose. That viewpoint certainly never helped the situation.