Ecumenism as understood by the holy Metropolitan Philaret who was the First Hierarch of the Russian Orthodox Church Abroad from 1964 to 1985- amicable relations with other faiths which does not betray the truth of Orthodoxy.
This is in fact the attitude which prevails today, now that we have put behind us the excesses of the 1960s and 1970s.
A delegation from the Russian Orthodox Church Abroad to Vatican II was sent by Metropolitan Philaret.
Metropolitan Philaret wrote to Patriarch Athenagoras in 1965:"Of course, we are not against amicable relations with the
representatives of other faiths, since this does not betray the truth
of Orthodoxy. For this reason our Church at one time accepted the
friendly invitation to send an observer to the Second Vatican Council,
just as it had sent an observer to the Protestant conference of the
World Council of Churches. . . ."
The letter, in the original Russian, can be found here:http://www.romanitas.ru/content/filaret-vozn/epistles/athenag1.htm
Metropolitan Philaret said he was not against "amicable relations with the representatives of other faiths, since this not betray the truth of Orthodoxy" and explained that this was the reason the ROCOR sent observers to Vatican II just as it had sent observers to the Protestant Conferences of the WCC.
Actually, there were more than one official observer representing the Russian Orthodox Church Outside of Russia at the Second Vatican Council. There was a full delegation, led by Archbishop Anthony of Geneva, and including Archimandrite Amvrossy (Pogodin), Archpriest Alexander Troubnikoff and Archpriest Igor Trojanoff.
All of them participated in the ceremonial Procession into St. Peter's Cathedral in Rome, together with the official delegation of the Moscow Patriarchate, headed by Archbishop Nikodim (Rotov), and representatives of seventeen Orthodox and Oriental churches, to pay their respects to the Pope and the Council.