I would argue for yoga, especially for styles that are principally standing postures (.e.g Bikram-esque). Postures like tree pose, dancers pose, standing forehead to knee, etc. Other benefits:
-core stability improves
-increased flexibility (which could only help should the athlete fall when snowboarding, for example)
-balance out the R and L sides of the body – since snowboarding is an “unequal” sport in terms of which leg is always in front etc.