Can't help on the inhaling food part, my dogs don't do it!
But on the snapping at treats-Hazel used to do that until I bit it hard in the rear. She wasn't doing it aggressively, she just didn't know any better.
I started with putting the treat in my fist and making her lick it out. She couldn't eat my fist, but if she wanted the treat she'd have to use her tongue (no teeth!) to get it out. I told her "Gently" throughout.
I then moved up to no fist. If she tried to snap, I'd pull my hand back and say "Gently", first softly, then firmer. Again and again and again until she took it gently.
Now she doesn't need reminding and takes all of her treats very gently without snapping at them. Occasionally on big or especially tasty things (like big bones) I'll say 'Gently Hazel' before giving them to her.