I'm the dedicated jungler for my team, and practice often in normals, if not every game. What I noticed is that most people aren't custom to seeing a jungler in 3s. So, they end up panicking that they're going going to lose their lane and that the game is over at that point. Let me be the first to say, this isn't the case. Normally, I start at one of the two lesser camps in lower jungle, but you can really start at any lesser camp.
My suggestion is this... don't pick a jungler who has weak ganks and minimal CC (Shyv has good damage, but no gap closer other than her ult and no cc.)
Like others have said, TT is about ganking. If you're jungling, you need to be able to jungle and gank in an effective manor, mostly helping out bot. (of course there are exceptions).
People who have great jungling potential in 3s (this is my opinion):
What I normally do, is start jungle, gank around 3 (When I have all my skills except ult), then stay in lane for one creep wave, and go back to jungling. Here's the deal as a jungler, though. You're going to progress at a much slower rate than the lanes. You need to be on top of warding. I buy pink wards all the time, but if you can get an oracles and stay alive, then vision wards will suffice.
It's just about knowing your champion, what you can and can't handle, and how often you need to gank. It is viable.