How to get rid of hub play in XTR FH-M975?
The advice that there should be play in a QR hub before tightening the skewer is true for a very high percent of QR bikes in the world because they have standard M10 or 3/8" steel axles, which flex under the load applied by the QR.

Many higher end hubs have oversize axles, usually aluminum, that see little or none of this flex and need to be adjusted as such if they're adjustable. FH-M975 is certainly in this camp, as are a lot of Shimano's higher end hubs from the last decade.

A good test whenever there's uncertainty is to adjust it so there's the smallest perceptible bit of play and observe what happens as you close the QR lever down. It's moving 180­° and it should start hitting resistance at 90°. What you want in an axle that does flex is for there to be play remaining at the 45° point but for it all to be taken up in the last 45° of movement, or the last quarter of its total movement. That will give you an essentially perfect adjustment on any QR hub and is also a test for whether the axle stiffness is such that it gets compressed meaningfully from QR forces. In other words, if you find that the play is unchanged from QR compression, you should then go back and adjust it so that all play is removed off the bike.