There's some characters that I never really played with (mostly the voiced, evil dude from the temple).

I'd like to get him without the restriction of being an evil sob. What would be the easiest way to achieve this?

I found the optional component of this mod does exactly what I was looking for:
https://www.moddb.com/games/arcanum/downloads/no-charisma-limits-to-new-followers-hack-for-uap-202

It works as a standalone w/o the charisma mod

AFAIR, if you have Persuasion Master training, any followers will join, regardless of your M/T Aptitude, Alignment, etc. It should also suppress any negative reactions from other followers in your party.

Charisma affects max. number of followers in your party and is needed for recruiting in some cases (e.g. Sogg in Shrouded Hills can be recruited with min. CH 9).