If you do any jumps at all I'd avoid Shimano's hollow crank arms. Ask me how I know.
I've been running Shimano XT (older Octalink and current outboard bearing model) and Saint cranks on my bikes for a while know and haven't had any issues and my tires leave the ground on occasion. I also know many DH riders use XTR cranks for their race rigs.
You must be talking about the super old XTR's. I had the XTR series two's that have hollow crank arms. These are the shinny gun metal colored cranks that the finish wears off of if you look at them wrong. I've also noticed DH guys running the old XTR's.
I still have the left crank arm with new hardware, BB (needs new phil wood bearings), and the chainrings. Wonder if someone could put any of it to good use?