Being a noble rogue is totally fine.
The problem is being a lv1 vampire rogue. So the tadpole make him lose his sunlight sensitivity, but he also loses his regeneration, resistances and the ability to climb on walls.
In PST and MotB we had very unusual companions and the game cared more about the story than balance. So we got a floating skull, a living armor, a soul construct or a bear God, to name a few.
If they do not want to give him vampire powers plus rogue powers, then the alternative is to make him a (not undead) slave of a vampire. So a vampire lord has forced a noble elf rogue to work for him for 200 years and the tadpole only removed the mental control of the vampire over him.
Prof. Dr. Dr. Mad S. Tist
World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already