I am level 33,and I rushed out and got my succ at 20 and FH at 30 and I still use VW almost exclusively in PvE.  Yes, if you add an immolate on top of CoA and Corruption, and then follow with rapid Shadowbolts or searing agonies you will draw the aggro off the VW, but by that time the mob is usually at death's door anyway.  If your VW loses aggro, and the mob is still healthy just run for a few seconds and the VW will regain aggro, meanwhile your DOTs are taking the mob down.  Of course, I'm affliction specced because as far as I can see DOT= warlock, so my DOTs are doing optimal damage for my level, so all I'm really arguing is that VW is affliction lock's best choice. 

I am admittedly not the most experienced and expert player and your experiences may well vary, but this has been my experience so far.