Yes, I myself wrote that Sayyid Musa al-Sadr was the one that declared them to be Muslims (I even wrote this some time ago - just ask
@SALMAN F ) but it was a misplacement by my part.
I am sure that you know the history of Al-Husseini. He was more of an Arab nationalist (politically active figure) than a scholar. Nor was he particularly famous for his scholarly work. He is most famous for his politics.
BTW those decisions were politically motivated (both of them). Before that you will struggle to find a single Muslim scholar of the time (Sunni as well as Shia) that considered Alawites (Nusayris as they are also known) to be Muslim. If you take a look at their teachings it is impossible for them to be Muslims. If they are Muslims Baha'i are Muslims too.
https://en.wikipedia.org/wiki/Bahá'í_Faith
If you take a look at leading Shia forums (Shiachat) prior to the Syrian civil war you will see most ordinary Shias on that forum agree with Alawites not being Muslims due to their beliefs and practices. BTW the old pre-Al-Assad constitution of Syria stated that Nusayris are a religious minority of their own separate from Muslims and Christians.
But let us return to the topic our we both might risk a ban for discussing religious topics.