If they have a Pagan name, who is their Patron
Some pagan names are saints' names as well (there is a Saint Aphrodite). Most, though, celebrate their name days on All Saints Sunday. As a whole, we don't really do patron saints much.
As someone who has a pagan name turned saints name in general no, I don't disagree with the Greek practice.
It is. Based on the notion that 'someone of that name is a saint known only to God and not to us'
I do however find that idea harder to apply in areas where there have not been thousands of years of these 'saints unknown' to draw upon. In areas where Orthodxy is not a historical long term presence the notion that there is a saint by a pagan god's name who is a saint is harder to believe.
As a convert ( since we are really talking that here) I couldn't pick such a name on a 'well there could have been a Saint Loki, we just don't really know'.