The -rech effects of Psi works really well with many of TA's debuffs and obviously the damage on Psi Blast is also really good 
Unfortunately you can't set Oil Slick ablaze with any of the Psi powers but if you take the Magic Origin then Apprentice Charm works, or you could take Power Mastery or Elec Mastery as they would both work too
The tech origin tazer can also ignite the oil slick.
And Fire Mastery of course.
I really should do something about this signature.
Apart from that Defenders don't get Fire Mastery. 
But yes, Tazer Darts can ignite Oil Slick. Also, you can stack an immob and disorient together for a psuedohold (well, you can with Psi Blast on its own, Subdue > Will Domination).
Do they not? Poor little defenders.
/TA controllers FTW.
I really should do something about this signature.
I can't say much about TA/Psi synergy even once i had one.
Here is the facts from my experience.
1- Soloable TA defender
2- One of the most fun toons i've ever created*
3- Also Magic Origin works fine for Oil Slick.
* I've deleted him like other toons upon my leave. Yeah i have regrets now but don't have that much love for the game mechanics (nearly can't play the game) to create him once again. Instead i have a Archery/Fire Control blaster whose stuck at lvl 4.
Making a TA/Psi defender atm since I really want a TA defender and I've used up all the other secondaries so I was wondering how well the two sets work together.
I'm thinking the -res from acid arrow will go well with Psychic Scream.
Also is there any chance oil slick can be set on fire by psi damage?