I cannot respond if Activision would respond to this or not and I somehow doubt it is a faulty disc if the rest of the game plays fine. Some ideas though:
Takes out the disc and GENTLY clean it, well first look at it. If it has any scratches on it that could be the source of your problem. And to answer your question no they will not replace a scratched disc. But again, gently clean it preferably with a mild cleanser and a microfiber towel (not ammonia and a paper towel)
Make sure there is no residual dust in your PS3 as well, give it a thorough checking
Change your customized loadout before the mission starts. I had a similar crash problem and found out it was because something I had in my customized load out was causing a glitch of some sorts. Changed it up and worked like a charm.