That doesn't mean they can't be useful, and they do already have a chip on their shoulder wrt Iran because of Iran's support for the Houthis.

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.

well with all the oil money, saudis and UAE don't even have to send their own citizens:

they can just pay gurkha mercenaries for the job

Did that involve boot on the grounds or just shelling via cruise missiles or from air? Also, Yemen is poorer, but has more or less the same population as Saudi Arabia.