I also run 8 speed XC Pro thumbshifters with an XTR mech and cassette and it works perfectly. They are more refined/better finished than the workhorse-style Shimano XTs.
The best thing is the front shifter though---it does a really cool ratcheting that the Shimano doesn't that I really like. Def the highlight for me.
Do the seven speed XC Pro shifters have a ghost click? I run seven speed XT thumbies with, again, an XTR mech and cassette on another bike, but if you are going to search them out, I'd say the 8 speed Suntours are a better bet. They have a little mark that says "7/8" with a orange dot over the "8."