I actually think Javik is a prime example of why the conclusion to Mass Effect 3 just rubs me the wrong way.
Some questions are just better left unanswered, imo.
But yes, somewhere in my first playthrough, I started using him as a squad member. I can't remember what is power is called (dark something?) but I remember if you upgrade it correctly, it's actually quite powerful when used on groups of enemies because it jumps to a different enemy when the first one dies.