Don't know about the marine betta, but I have a blue throat trigger and a jawfish in my 140. There's never been any aggression between the two as they both basically just mind their own business and hardly seem to notice each other. As someone else mentioned, the only thing to keep in mind with these two is that the jawfish won't venture far from it's burrow, so it needs to be spot fed. Otherwise the trigger and other aggressive feeders will nab all food in the water column before any reach the jawfish's range.
BTW, my jawfish is a tiger, not a blue spot, but I would think behaviorally they should be pretty similar. The blue spots have a reputation for being hard to keep, but this one is about as hardy a fish as I've come across. He disappeared a few days after I got him so I thought he got stressed and died before ever making his burrow. Then almost three weeks later, I noticed him in the return chamber of my sump. To get there, he would have had to jump into the overflow, ride down the drain pipe, avoid the skimmer, cross the refugium, then jump into the return chamber - all without any food other than what he may have found in the fuge. He looked like a concentration camp prisoner when I found him, but after being put back in the display, he finally found a good spot to burrow and has plumped up nicely. He's actually my favorite fish now and is the guy in my avatar. [smilie=smile.gif]
