On January 25 and June 21 1867, the Holy Synod of the Church of Russia issued decrees that stated:
"In those places where there are no Greek-Uniate Churches and clergy, Orthodox Priests are granted the right to perform Needs and Mysteries for persons of the Greek-Uniate confession, when the latter shall ask them about this."
However, the date is 1867. I know that Metr. Antonyi Khrapovitsky, spoke out srongly against this in the 1890's.
I may be wrong, but I believe this decree was revoked as a result. Also, a special service was devised for admitting Greek Catholics to Orthodoxy. Previously, I believe the service for admitting Roman Catholics was in place.