Yemen situation is just good indication of how useful they could be, and answer is not much. They don't have good functioning military.

Their military is a paper tiger like Saddam’s was during the Iraq invasion. Modern gear but without the doctrine or officer corps to effectively use it.

My experience while working there years ago was that their armed forces were a weird mix of coup proofing and a nepotistic dumping ground for family members who couldn’t be trusted to help run the family business.