Vermin without an intelligence score can actually be a bonus. If you want to give them intelligence then you may as well stick with vanilla hunter. The fact they lack intelligence actually means they are immune to mind-affecting effects. The Praying Mantis is really good for pinning down your enemy so you can pick on them. That's why you can actually get Precise Shot as a bonus feat. The companions' design is to hold down your enemies so you can shoot them. You could also go flanking though. I would put ability score bonuses into constitution, as that boosts the poisons. Also, bonus tricks should be enough for this. You don't really need the companion to do that much you can't just push it to do.
If you are only missing out on one or two feats, mindless isn't that bad. But by 3 feats, you will pretty much have to put a point into intelligence or you miss out on too much.
If you dont mind being a little heartless, get eye for talent, and put the boost in strength. Then when your companion hits 5 hd, kill or release it and grab one with the boost to intelligence.
Well, if you aren't real quick with applying healing, die hard just encourages the enemy to hit you again when you are at negative hp, so I would look at other feats. Weapon focus in either claw or grapple (I believe that focus in claw should add to your Grab CMD), ability focus in poison to boost the dc, or power attack would boost your offense. If you are worried more about defense, shore up whichever save seems most important in this campaign, probably will, maybe fort. Combat reflexes and bodygaurd could be cool to boost defense for your hunter.
I also don't see enough tricks listed, do you have them all trainded? Remember that you can teach skirmisher tricks to Mr. Stingy, some of them are kinda fun.