I think Iran joined in later by sending some drones, but their involvement seems a lot less than the UAE.

The UAE like Saudi Arabia hosts many American military bases and gets American weapons. But I'm still not sure if this is an American proxy war through the UAE or the UAE doing this by themselves.

The UAE does have a lot of sketchy stuff going on though they're looking a bit like a convenient black sheep: American mercenaries hired by UAE to kill in Yemen - BBC World Service Documentaries

Iran provides some support to SAF likely because Sudan is next to the Red Sea and they don't want Sudan to fall under control of a Western aligned regime.

Once again my knowledge of this conflict might be completely off this is just random stuff I picked up. Don't take anything in this comment as the truth.