I don't think the choice of mech will have much to do with it, assuming the cable pull is the same per click with shimano and suntour systems. Since the suntour cassette has two different spacings, I imagine the thumbies will pull a different amount of cable, depending on the position they're in. The difference is the same as between shimano 7 and 8s - 0.2mm per click. I think the floating jockey in shimano mechs should eliminate this difference and allow for decent shifting, although intial setup might be a bit trickier.
I've seen a few threads now where people hace used suntour thumbies on otherwise shimano drivetrains without problem, and I think even som manufactureres (kona?) were speccing this setup onthe bikes BITD.
I might get chance to set it up this weekend, but can't ride it until I get my front brake
I'll report back once I get everything working (or not!)