Seems as if there are issues on both sides.
1) A 5 YO CAN learn table manners with a lot of repetition; it will take constant reminders and, yes, some amount of punishment. That's okay.
2) You definitely need to back him up in front of your son or he'll spend the rest of his childhood playing you against your hubby and never learn to be civilized.
I had the opposite problem. My hubby wouldn't let me discipline my son, and it frustrated me to no end when he'd counter a punishment I'd given. I had to divorce him before I could civilize my child (He's now a very well-behaved, happy little boy). Don't let that happen. Your job is to be his parent, not his best friend.
3) Your hubby definitely seems to be overreacting, and it's definitely not getting him the desired outcome. Everyone who mentioned discussing it when your son isn't around made a good point. See if you can figure out what punishment/reward system you will use at the table, and agree on it. Maybe that will keep your husband more focused and he won't react out of anger. Then, you will definitely find it easier to back him up.
Someone else mentioned having hubby spend some positive time with your son. Good point. Kids WILL vie for any attention they can get...even if it's negative.
This seems like a fixable problem. Unless there are other issues, y'all should be fine.