While not inherently dark sided as far as being a member of the Imperium, Kholvar does have a particular hatred for Jedi from his upbringing with the Zeison Sha, and is a pretty evil dick.
Might offer some more insight to different kinds of evil outside of the typical acolyte's motives. If it's not what you're looking for, its nbd. :3
Well, he needs know how "dark" is the dark side, someone that truly is a darksider.
It can be in a talk, expressions, and even a fight (with no death or maiming)