Can't confirm, it's a general assumption given some of the damage numbers I've seen floating around. Namely after looking at Ruke in his damage reduction equips on NIN. He has some pretty low NM grade hits that I presume point to a post-VIT/DEF calculation:
http://img227.imageshack.us/img227/7168/faith1qm.jpg
I suppose it could be tested by taking a reasonably large population of hits, say 100 each, with the four conditions of:
base (no dmg reduction, no +VIT/DEF)
base + dmg reduc
base + VIT/DEF
base + dmg reduc + VIT/DEF
You should be able to discern where the damage reduction percentage effect applies given the numbers.