It's not so much the hair getting caught in the mask, but the hair interfering with the seals the masks make with the face.
You see, besides the speed jeans, when pulling high G stunts, the mask actually forces air into the lungs. Can't have it leaking around the face rather than into it. The latest "Combat Edge" systems consist of special gsuits, vest, helmet and mask - during the maneuvers, the helmet tightens up the seal between the mask and face (thanks to a little bladder near the back of the helmet that inflates).
(Meaning the Blue Angels have it even tougher - no gsuits and masks, but all the high-G pulling stunts).
It's all done so no one suffers from GLOC.
Of course, if you were a seal, you wouldn't want your mask to start leaking water in, too (or have it bubble in - that's gotta be distracting).