Is he still Ukrainian Orthodox?
Dispensations from Canon 874 are generally understood when either an Orthodox godparent participates in a Catholic baptism or a Catholic participates in an Orthodox baptism in light of Unitatis Redintegratio and Orientale Lumen.
I agree entirely with Fr. David’s post above, and have assisted at several of these over the years in the Ukrainian Catholic Church.
Quite a few Ukrainians who were baptised in the Soviet era were Greek Catholics baptised as Orthodox simply because that was the only available church for baptism. It is not unheard of for one of the parents or godparents to be Ukrainian Orthodox at a Ukrainian Greek Catholic baptism.
The Church definitely looks at this quite differently than if the godparents were Protestant or non-Christian.