List 62: Abyssinian and Horn of Africa: The notes say that a Muslim ally-general cannot command Ethiopians. However, the only troops defined as 'Ethiopian' are the Bd (F) Sarawit and the Hd (O) camp artisans. Does this mean all other troops in the army can be classified as Muslim if desired (and thus be commanded by a Muslim ally general)?
I believe so. It certainly would make no sense if Muslim generals couldn't command horsemen and tribal levies.
As there are apparently no restrictions on Ethiopians commanding Muslims, does this mean a post-1285 Ethiopian army can include Muslim Cv (O) (as long as no generals are so upgraded) and Bd (X) Muslim dembus wielders?
Near as I can tell, yes.
Also, Bw (I) can be upgraded to Bw (O) as Muslim archers. Does this mean Bw (I) aren't Muslims?
The most natural reading would seem to be that Bw (I) can't be Muslims, but it really could be clearer. Whether a Muslim ally-gen can command non-Muslim, non-Ethiopian Bw (I) - they could be still-pagan Somalis, frex - is anyone's guess.
Finally, what's the distinction between Abyssinians/Ethiopians and Axumites/Solomonids? I get the impression the Solomonid dynasty replaced the Axumite dynasty in 970, and that Solomonids are not Muslim, but these points are far from clear in the list notes.
For list purposes, Abyssinians and Ethiopians are the same thing, and Solomonids are non-Muslim (specifically Christian).
"Axumite" (a/k/a "Aksumite") properly refers to the capital (Axum/Aksum) or the kingdom rather than the ruling dynasty. It declined in the tenth century (the list chosing 970 as the end date - probably as good as any), to be replaced by various Christian, pagan, and Muslim statelets, among which that of the "Solomonid" - claiming descent from Solomon and the Queen of Sheba - dynasty gained preeminence in the 13th century.
The dynasty stuck around (with some interruptions) until 1974 when it's last reigning member, Haile Selassie, was deposed.