If you want to go for Passive/secondary oriented set yeah as far as i know (from my ill/thermal) or see that sets works together pretty well.
With Empathy i think you will want whole set. For illusion other than your pets i suggest you to take Greater Invisibility and Group Invisibility. If you can find a place in your early build, Recall Friend will be very helpfull to you. You can ghost missions in TFs, teleport and rez your fallen team mates in a safe zone etc.
My personal feelings from ill/thermal is, it is not worth it. I am not a person who can play an Empath/Thermal. This is why i re-rolled an ill/rad to enjoy illusion. Keeping eye on everyone's health bar and trying to keep everyone Thaw'ed. Looks like my worst nightmare.
So i am repeating again, if you want an Empath more usefull for a team, go for that build. If you want to play illusion and focusing on controling more, pick another secondary.
The damage side of things is pet heavy, so in most situations you can throw in your pets to help the team and then focus on healing/buffing with your emp powers without really losing much. You've effectively an invisible healer, so can really get away a lot, and unless you're overly blatant, or stand in the middle of aoe, then you'll almost never get hit by mobs.
If the team has a fair few healers, or not taking much damage, then you're free to play with your ill powers a bit more. Take advantage of invisibility and deceive to mess with the minds of upcoming packs.
A fun combination. 
Hello all , im planning on makin a full support class based on illusion / emp .
Am i wasting my time over this , or theres some sense in this arch .
Hints more then welcome
Tks all in advance