If you are not aware of Plogue Bidule - and for those still waiting on Native-Instruments to get Absynth2 RTAS ready (they keep delaying it it seems), you can use it NOW along with any other VSTi, using Plogue Bidule in rewire mode into ProTools.
It's awesome!! I can't beleive how well it works and currently it's still FREE (beta testing but pretty dang solid!!)
Check it out!! Tempo/BPM sync and the whole 9 yards. Works like a champ.
http://www.plogue.com/bidule/index.html