shimano put a patent on their bottom bracket because they didn't want anyone to make compatible parts. RaceFace got around shimano's patent by having the non-drive arm fixed to the bb axle instead of the drive side like shimano did. so raceface has made the effort to make compatible parts, not shimano
by fixing the bb axle to the non-drive side crank arm, raceface acutally has an advantage over xtr. with xtr, because the bb axle is fixed to the drive side, if anything goes wrong with the drive arm or bb axle then the unit as a whole is much more expensive to replace than if the axle is fixed to the non-drive side. This is how raceface explained it to my local shop mechanics when they went to the bike show in Montreal. other than that, they are the same. the axles are the same diameter and length and so the bottom bracket cups with their outboard bearings are totally compatible with xtr.