Trust me; I know from personal experience. Put a Race Face middle ring on my '07 XT crank and it wouldn't work no matter what I did to it. Skipping under load, missing the ring on shifts, all kinds of annoying stuff. Put the Shimano steel/carbon on it and all was good again.
Besides, why risk compatibility problems when the Shimano ring works great, is reasonably priced, doesn't have a significant weight penalty, and because the teeth are steel, lasts through 2 big rings and cassettes?
I only had problems when I was really putting the hammer down, so maybe you weren't riding hard enough.
XT and XTR rings are interchangeable, so that would indicate that XT requires a Shimano ring too.