To add further:
After reading motherboard manual I've discovered that the board have one PCI-E 1.0 socket and the card has started in it (inserted with no 1U chasis cover placed). This fact didn't helped because there is no raiser card for that socket for that 1U server.
So the answer discovered in experimental way is: not compatible. But more info from experts on compatibility of different versions of PCI-E is wanted, so the question remains.