Hello again, and thank you all kindly for your advice. DH has made it clear to his mother that she is not invited into our home until she learns how to behave herself. She didn't apologize, but did actually listen to DH and admitted she needs to "work on some things." I think that's as good as we're gonna get.
As for DH's profession, he likes to think he's Batman - he works at night, has a "utility belt," a closet full of "costumes," and a nifty car with all sorts of gadgets (lights and sirens mostly). It's what he wanted to do ever since he was a kid, it's not like it was a huge surprise to her when he was hired with his department.
To the poster who asked about his siblings, yes. He has an older sibling who has MILs only other grandchildren. She's been banned from their house numerous times for harassing them about politics, and passive aggressive acts ("accidentally" breaking things, "accidentally" giving the kids things they're not allowed to have according to their parents' rules, etc.). This seems to be something that happens when grandkids come into the picture. She left us alone until my son came along, so I never really thought about how clearly off her rocker she is. I'm sure she's concerned for her son's safety, and in her mind, his conscience, but she really has a funny way of showing it. I don't think she's a bad person, she's just...off.
Thanks again for the help!