Engaged model making ZOC Dodge

I'm not seeing a reason you can't. Engaged only references that you don't have LoF other than to models you're engaged with, and that the only way to leave engagement is via dodging.

 

It'd also always be at least -3 due Dodge with active trooper outside of LOF unless the active Trooper enters S2S.

It's a distinct buff to Stealth.

 

Yes, because Stealth doesn't work vs Troopers with 6S (so the requirements or 6S are irrelevant).