Personally, I think that whomever YOU want to have in there is fine. YOU are the one that is going to be uncomfortable, possibly in pain, "exposed", etc.. If you are comfortable with your mom being in there and want her there, then talk to her and explain why your husband is hesitant. Maybe if he knows that she understands her role (support for BOTH you and your husband, and she is not the parent of the baby being born) then he will relax about it. Set boundaries for her. She can be in the room, but only background.. your husband will be holding your hand and RIGHT THERE and she is not to interfere/impede anything he is watching/doing, etc.
For me, I didn't want ANYONE in there except my spouse, and my spouse suggested letting his mother come in. I said NO. He wasn't happy, but accepted it over time. She wasn't even in the city when my son was born. So it became a non-issue. MY mother was, but I didn't want her in there either. Both times with both kids, it was just me and him. And everyone was fine with it.
It really is what will make you most comfortable. You need someone who will be YOUR advocate in there... helping YOU to relax and asking questions FOR you so that YOU understand everything that is happening (birth plans don't always go "as planned"). If you define your mother's role as supporting your husband so that he can support you, maybe you can all benefit.
If having her in there will cause stress for you, worrying about how your husband is feeling about it, or worrying that she might overstep or whatever, then it is not worth it. You need to be relaxed and focused only on delivery.. not the extraneous "feelings" that might result from who is there and who is not...
Good luck on this one.
May I add as one of the other posters mentioned, that 6 months is a LONG time for mom to stay with you afterwards. Frankly, if you want Dad to help with the baby when he/she is 8 months old (and really trying your patience, etc) then he needs to be helping regularly from day one. Otherwise it won't happen. And if Mom is there for 6 months, Dad will not be helping much, Mom will. I would suggest maybe a week or 2. By then, you will have adjusted to lack of sleep and be able to repare meals and do laundry, etc.. and hubby will have figured out how to help with feedings, diapers, soothing, etc. I hope and pray your mom is like mine was, and was extremely aware of how important a time of bonding this is for the mom,dad and baby. And steps back and only "helps" when you ask her to... my mom did most of her helping by sweeping the floor and washing clothes rather than directly with the baby. She was a Godsend! Discuss this thoroughly with her before the arrival.