My husband lost a filling and his tooth broke off over 6 months ago finally went to the dentist and it is infected. Could he have blood poisoning?

Probably not. Most dental infections are localized and are limited to the immediate area. I'm glad your husband finally went to the dentist. Moral of the story: don't wait until there is a problem. Get regular exams from your dentist. It's far easier to prevent a problem than to treat it. And cheaper too!
Not likely. But any infection can spread. There is a reason for routine dental care, just to prevent scenarios such as this. I hope your husband's treatment works out well.
It's unlikely. While an infected tooth can spread infection throughout the body, its rare.
Maybe but not likely. It's possible. However, if he did, he would have fever, sweating, weakness, etc. Just a sore, swollen, infected tooth doesn't mean he is septic (fancy medical word for "blood poisoning"). It is something to take care of aggressively, though, to make sure it doesn't go in this direction.