There are some exceptions in pre-schism saints for mutual veneration. They venerate Pope Nicholas I, we venerate St. Photios the Great (although some Eastern Catholics venerate him, too).
I imagine it's the date of canonization, not the date of death, that makes the difference between a "pre-schism" and a "post-schism" saint.
Well, in the above-mentioned case, Pope Nicholas 1 was, IIRC, venerated right after his death. But he was the nemesis of St. Photios, so he doesn't get on the list.
Date of canonization is tricky. In the East, the first saint to be formally canonized with a service was St. Gregory Palamas, so I read somewhere. Before that in east and west, the process was much less formal. So, on the Orthodox principal of public veneration, there are pre-schism Western saints we could accept (if we ignored those who bicker) who were not formally canonized until after the schism, or not formally canonized at all. But I think, for purposes of order, a local holy synod should make a ruling formally.