So, if I were to donate to Toribash, would I still be able to get the +mark sign in front of my name in-game, or is it impossible?

probably not

Getting the + is impossible now it is for people who bought this game in 2007 (I think) only

Highly doubt it, + is reserved for the old-schoolers.
Buying your way into it would tarnish the exclusivity of the group.

Alright, I was just wondering mostly, as people kept telling me you could still get it when I asked.