My main is a lock. In northrend, I was able to solo almost all of the group quests I attempted. First one I had issues with was the "ring" one at Grizzly hills...but that was due to fighting the mechanical thing who doesn't follow aggro rules. VW isn't brilliant at tanking, but when you get the felguard it's just awesome.

I can't remember the name of the quest, but it was in the zone North of Icecrown, where you had to fight into a church type building then fight an uber strong elte at the alter. I was able solo the quest. Don't get me wrong, it does take a while...basic tactic is put corruption, curse of agone and immolate on the mob.....then keep healing the demon. Life tap every so often to replace the demon's mana...then life drain to replace your own.

So with a priest there, you can heal the lock everytime he life taps. My suggestion would be to level the lock as affliction using the VW as a tank until level 50 then switch to demo to get the felguard. It would be up to you what you want to do with the priest....whether that be helping with the DPS as shadow or healing as disc/holy.