I'll have to check the value of the sugar beetle meat, it's *supposed* to be higher. Not sure why you're not getting anything when you slaughter them, though, they seem to work fine for me. I'll run some tests on it, though.
Cave Crabs are better than dogs but still not great at dealing with enemy warriors in armor. Good for random snatchers and marauding critters, though. I may have to do a crab-intensive fort and see just how many I can throw at an ambush. It'd be interesting to see how well they do.
Giant Beetles are pretty much a 1-1 match for most opponents. I've had two dwarves and a few beetles hold off an entire ambush of goblins, and the beetles got their share of the kills. Elite soldiers tend to smack them, of course, but they don't lose too much otherwise.