If that undulated is alone in that tank, he's going to be hard-pressed to let anyone else in there.
As for a wrasse, a sensible choice would be the lunar due to it's speed and activity level. That's not saying it won't be stressed if the undulated decided to chase it relentlessly.
I work at a LFS, and we've had a 4" undulated trigger brought back 4 times already due to agressiveness. Just thought I should let ya know.
