Flower, WWM mentions that only one should be kept in a tank, but anecdotal evidence suggests that these two MIGHT coexist peacefully. Probably you'd have a better chance if the newcomer was larger than the existing fish. My guess from a quick online search would be it's the luck of the draw.
And Lois, yes I'll get a picture tonight. He's actually picking at the algae on the rock, and sifting sand...he even found a buried mysis shrimp that I had missed in the tank cleaning (eww) that he started picking off of. I removed that after a few minutes though, because....eww. He's still got a concave belly, which is a small concern, but if I can get him eating meaty foods I won't be quite as fussed. I'll consider worming him if I don't see that belly fill out. I'm just happy because he's MUCH more active than the last one, which is a good indicator of health in and of itself.