Can someone clear up my confusion with this question please.
Some lists allow you to take allies who have Brilliant/Inert C-in-C's during the time period your allowed to have those allies i.e. Later Visigothic can have Early Byzantine allies during the time frame Belisarius is around.
In this example could I take Belisarius as the Ally general for the Later Visigothic?
I'd say yes, based on the following reasons:
1. There is at least one case where it is specifically forbidden - Early Armenian allies for the Mithradatic army can't be led by Inert Tigranes. If not forbidden, it should be automatically available.
2. There's no geographical limitation on Belisarius's use. By contrast, for example, Inert Lepidus couldn't command Marian Roman allies in a Later Judean army as he was only active in Italy and North Africa. But Julius Caesar could command Marian Roman allies, as there are no geographical limits on his use.
Having said that, I'd much prefer to use Belisarius in charge of an Early Byzantine army than as an ally in a Later Visigothic army, because he has so many more options in that position.