After the little dustup over adding vampire templates to nontraditional monsters, obviously I did a lot of research as did others... and check out who did it before: none other than SEAN K. REYNOLDS!
Yes, in Ghostwalk he premiered the 3e concept of Monstrous Vampire as an acquired template, allowing vampiric dragons, vampiric gibbering mouthers, vampiric bears, vampiric grigs, vampiric kraken, and vampiric bats!
Check it out here: http://www.wizards.com/default.asp?x=dnd/we/20031225a
There was a Vampric Gibbering Mouther in one of the iconic 3e adventures, Heart of Nightfang Spire. It actually had a decent 'explanation', if such a thing is possible.