Wow, this dragon looks a lot better than my typical half-assed attempts. Looks like you haven't tossed tremorsense into the statistics block yet, though. If you want my two cents, I'd say only let it use tremorsense while burrowed.
You might want to consider giving it track as a bonus feat. I know that most of the big cats don't get this feat, but they tend to have a decent feeding ground, and also can stay within fairly close proximity to their prey without being very visible, thanks to the dense jungle (for tigers) or high grass (lions). I don't really see any feeding ground being able to sustain one of these guys once they get too big, and grass can only grow so high. Even if, once they get too big, these dragons only hunt while burrowing, they'll still need to find the area their prey is in while above ground (being deep enough underground not to freak out anything above ground would mean that the tremorsense radius would be good for pinpointing prey, not finding it initially). Because they won't be able to get close enough to see their prey (if it can see the prey, the prey can likely see it), they'd need to rely on tracking it down to get a general idea of where it is. While you're at it, you might want to toss on the scent extraordinary ability (I don't think dragons usually have this, but it would be a great idea for a ground hunter-type dragon).