Re: My husband hates my parents...
My first question is why he hates them and is concerned about his kids.
Is he worried for their safety? If there is any possibility of emotional or physical damage then thoughts below don't apply.
If he simply doesn't like their personality...he married you and you are their daughter, he loves you, so you might point that out, they helped create you.
If you divorced, you get the kids and will take them over to see them free and clear. Divorce takes all of his say away.
I would tell him they get a relationship with their grandparents, create a schedule/rules along those lines and ask for his input. Have him identify his concerns, and try to incorporate them to meet his needs. Like, if they are prone to racial comments...((just making this up!)) ask the grandparents to refrain in front of the kids, and have a conversation with the kids - age appropriate of course.
Perhaps that would help? It seems you are at an impasse, I would come up with a plan, open to some compromise, he can either participate understanding a "veto" is not an option.
good luck, Kes