> Saudi Arabia hasn't really been a us ally since

But then who has "really" been an ally since whenever? All sovereign nations have national interests, and they are not 100% allied with the US interests.

Still, in the case of Saudi Arabia, their most important security concern is Iran. And there, they are aligned with the US. Also, the US is the most important security partner of Israel, and, according to wikipedia [1], Saudi Arabia has quite a good working relationship with Israel

  However, reports have surfaced in recent years indicating extensive behind-the-scenes diplomatic, intelligence, and security cooperation between the two as part of a larger Arab-Israeli alliance against Iran (see Iran–Israel proxy conflict and Iran–Saudi Arabia proxy conflict) and, more recently, Turkey under Erdoğan. At the same time, the Saudi relationship with the Palestinian National Authority is deteriorating. 

A former general working for Saudi Arabia is in no way traitorous. It absolutely makes sense, both in their personal interest, but also in the general US national interest.

Yes, I know about Kashogi. But those guys are not going there to tell MBS to kill more disidents. They are going there to give security advice. And that security advice will benefit the US, not hinder it, because it will result in a stronger ally, not a stronger enemy.

[1] https://en.wikipedia.org/wiki/Israel%E2%80%93Saudi_Arabia_re...