Spoilers for Dark Urge questline - obviously.
In order to have Sceleritas Fel in your camp and initiate conversation with him, you need to kill Orin and embrace Bhaal.
If you want to know what happens if you lose the duel with Orin follow this link:
https://www.youtube.com/watch?v=HPiTCm3w-0I
Poor Cruor, you can find his body and a note in Orin's chambers.
My attire: Viconia's armour in a black and red dye. No mods.