Sorry to hear your dilema!
That's awesome that your mom is offering to pay for the photographer! You both should look at it as a great gift and contribution to your day. Your mom really wants to give you something that can last a lifetime.
Just talk it over again, I'm sure he will realize that it isn't a big deal. Maybe he is feeling a bit hurt, because his parents aren't able to provide such an amazing gift like the one your mom is providing :0(
I kinda understand both of your side thou, because my family is really involve and wants to participate and his family is not! I don't even think his parents are going to our wedding... only his 20 year old brother.... With that said, I decided not to accept any help until we are in Mexico. If my family wants to pay for the rehersal/welcome dinner or anything related to the wedding ones we are in Mexico, at that point I'll accept it, because at that point it will be a gift for the both of us (as husband & wife)....
Not sure if this helps, but best of luck with everything.