Well, as far as recruiting Spartan's and the level 4 government goes, consider this:

They aren't really a completely autonomous allied government, rather, they are a puppet state that you exercise direct control over, if not in name. Yes, you don't technically make all the decisions, but all of the big ones. Evidenced of course, by your garrisoning and conquering of that countries' capital city.

Let us pretend you are occupying Sparta. Would you want Sparta training The Ancient World's equivalent of the Delta Force? Especially when you consider it's highly likely that they'll be disloyal, and could give easy chances to start a rebellion.