Nicky, I have a couple of small suggestions. First, try to "catch him in the act of getting it right and bring on the fan fare." In other words, when he does the smallest thing that shows caring, respect, or even just consideration towards your mom, make a really big deal about it and let him know how much you appreciate it. That's the best way to shape someone else's behavior- positive reinforcement, not criticism for failure. You can consider thanking him for allowing your mom to live with you (even if his family members have done the same in the past!)
Secondly, I'm glad to hear he is willing to work on other areas of your marriage. You know, research shows that 60% of what healthy couples argue about is unresolvable! This means that you two might always have issues about family. The truth is, the good should outweigh the bad. Although he might never meet your expectations about your mom, he might be a good husband in other ways. You can still have a good marriage even if he is less than perfect towards your mom. I know you wish it were otherwise and so do I for your sake, but if it doesn't change, it might not be the end of the world. Once you start to mellow on this issue, I have a prediction. he just might start being kinder towards her. It's funny, but it often works that way. I sure hope it will for you. Michele
