The vampire Batman was just one of several alternate-reality Batmen that "our" Bats recruited to help him beat the Injustice Syndicate. They also included a Zorro Batman, a giant-headed telekinetic Batman, a cowboy Batman, a Hulk-type Batman, and a Batman in a high-tech armor suit. No doubt an homage to the many weird variations on Batman seen in '50s comics (the big-headed Batman in particular looked like something from that era), though some may be
Elseworlds homages.
Cool...by the way. In the B/B episode where BATMAN went to Owlman's world, they seemed to say it was EARTH 23...is that really a world now in DC's continuity? Earth 23? And is it like that, in someway, in the comics too?
It was loosely based on pre-Crisis DC's Earth-3, home to the Crime Syndicate, evil versions of the Justice League. Ultraman for Superman, Owlman for Batman, Superwoman for Wonder Woman, etc. The new DC multiverse that was recently created has a similar Earth-3. No Earth-23 has been seen yet in the comics.