Well, seeing how there are two "empty" slots in the "class completion" panel for dungeons, and Holy Diver will most likely be filling one of them. If he's a goat, I'd wager he'll fill the 4th monster slot leaving a nice slot for a guard.
Execept the guard would have to take the topmost position and then it would make thematic sense since the tinker could be in the same row as the rogue classes, the crusader in the same row as the priests and the transmuter with the wizards.
He could have the following abilities:
1) Persistance - keeps persistant appearance under all circumstances (meaning only one graphic representation
2) Keep going with all the good jokes I've seen around the forums of the same variety as the above one
3) Gets a bit more gold for sucesfully clearing out a dungeon (he's vanilla, right, should be an incentive to play him)
I'd say it'd be swell.