I think Verandis became a vampire willingly and did something horrific to gain Molag Bal's favour as a vampire lord - and for the most pathetic reason you could think of (not the characteristic lust for power). I think Molag Bal finds his little meow meow vampire so funny, he is his blorbo (pejorative).

Then consider the whole 'his bloodline is special' thing and I think Bal has this joke going on, like pure-hearted Verandis, let's give him horrors beyond comprehension (whatever Lady Essenia's transformation is meant to represent).