I don't really want to mix First Order and Empire pilots together, it just rubs me the wrong way.
Agreed. I'm not a fan either. But the option is there.
I actually plan on running Mauler Michel and Scourge outside of the formation
Hmmm...... They can operate on their own, but 'd rather keep them in the 'block', to be honest - unless you're facing an opponent you need a 'dragnet' to run to ground (dash rendar springs to mind), then you might as well make sure you engage en masse. Splitting up with TIE fighters is generally not worth it if you don't have to.
If you do want a flanking threat, I'd suggest backstabber instead - if he's running outside the 'block', his is the easiest 'extra attack die' pilot ability to trigger, and he saves a couple of points over Mithel or Scourge.