What's the deal with Ashara Zavros? From the bio there she seems like a Jedi companion, not Sith
A part of being an inquisitor is corruption and manipulation, being able to convert a jedi by sowing the seeds of doubt in their mind is some kind of power trip for the Sith. Palpatine corrupted Vader and tried to corrupt Luke as well. Perhaps it is the impact it has for the Jedi to have jedi faithful reject the teaching of the jedi way and fall to the dark side that makes it a tempting prize. Perhaps it is the psychological conquest against the opposite side more than the it is a conquest over the individual.