Can an oral surgeon prescribe a cpap?

Sure: Any licensed physician can prescribe a c-pap machine. Some physicians are obviously more adept at the specifics to the oxygen concentration, etc. Parameters that need to be associated with the machine. Pulmonologists and other specialist may do fellowships or get trained in sleep medicine and have familiarity with sleep disorders. If concerned, check with the surgeon and assure he is comfortable.

Depends: Depends on state licensure. Also probably credentials. Some oral surgeons are both physicians and dentists. Other oral surgeons have only a dental degree.