Yes. You can use a henchman or more than one at the same time, and you can also use your minion with henchmen too.
If you want everyone to be from the same school, then hire a henchman (or henchwoman or hench animal) from different levels. Such as: Level 40 Ice, Level 50 Ice, Level 60 Ice etc. Then you can also use your minion with any henchman.
At least, so far I have always been able to. For those who don't know how to hire a henchman: Just open the Crown shop during your turn at battle, to choose and hire a henchman.
The henchman only lasts for that one battle by the way.
