I run an Ill/Therm troller, and it is a fantastic combo. Not /quite/ the same as Emp, but similar enough I would think.
My opinion only: Illusion is the best pairing for Empathy in game, beating all Defender secondaries. I respect anyone who disagrees with this, again its my opinion only after playing many Empathy combinations.
Phantom Army is the anti-alpha and often means no need for a designated "tank" at all
Deceive/Confuse is not available to Defenders and is another awesome mitigation able to be deployed before the fight begins
Group Invisibility to the whole team and all pets with one click, which means easy stealthing and/or defense boost to all
To me those are the main three perks for Empathy being paired with Illusion vs other sets
Just... win
Global name: @k26dp