It's preferable with a suspension fork to keep the load off of the fork lowers to minimize unsprung weight for better suspension compliance and to reduce stresses. So a rack mounted to the frame or fork upper, like a Tubus Swing, would be a better choice than an OMM.

Why not have the best of both worlds? Remember, the Xizang was designed originally for a rigid fork. I bought one of these for my '93 GT Zaskar (Zaskars and Xizangs have the same geometry). It has the same geometry as the OEM GT rigid fork. For $41, you can have a rigid fork for touring with a front rack and keep the Judy for the rough stuff. Swapping forks is a 15 minute job.