My boyfriend is being released from the Clark County Detention Center in Nevada next Monday, the 5th of May. Before he was taken into custody, but while he was out on bail, he attended a semester of college at North Dakota State University in Fargo, ND, and wants to go back to finish school. If he were to get a part time job, live in the dorms, and attend school, would his request to transfer his probation be approved?

The offense involved alcohol and was really a matter of being in the wrong place at the wrong time. He is an excellent student and has the family support to afford college. He was originally supposed to serve 6 months of a Boot Camp program, but wasn't accepted due to not enough room at the facility, and is now being released on a plea bargain.

If he does get the transfer, will he be able to go back to Vegas for holidays and summers? Or would that have to involve a transfer back to the "sending" state as well?

No they will not keep "transfering him back and forth"

Yes most liekly they will but he will have to request it, and both states will have to agree. ( it will not be a overnight answer) Once it is approved he will have to go and report to the new state.
After he is in the new state, he will have to get permission from his PO there to tavel back to Nevada. Which again should not be a issue if he is not doing anything wrong.