Just like using aftermarket auto parts, there are legal issues involved.
Basically, Bushmaster would need to prove it was the ammunition that caused your problem. Tricky, especially if you didn't tell them you were shooting Wolf. Follow so far?
Now, the only way Bushmaster, or any other manufacturer, can cover themselves is to specify new, factory brass ammunition. They have no way of knowing where your uncle Larry's reloadings were made properly, so how can they warranty the gun?
Wolf falls into a special catagory. It's factory ammunition, but it's made in Russia where a group like SAMMI has no influence over the specifications, and it's steel cased with a lacquer coating. Not really what the gun was designed for.
Lot's of folks shoot Wolf. The problems tend to come in 2 areas:
1. it's dirty, slow and the lacquer can sometimes heat up and stick in the chamber. 2. it *might* wear some parts faster, such as the extractor.
So, you pays your money, you takes your chances. Is it worth the cost savings to you? If it is, shoot the Wolf and with the savings buy a few spares extractors. If it's not, take a look at South African surplus. It's full milspec ammunition, it's cleaner and faster than Wolf, and only a little more money.
Bushmaster is going to try and keep you happy. If the problem isn't related to ammo selection, you have no warranty issue. If the gun breaks, send it back. If it were provable that the ammo caused it, pay Bushmaster to fix it and you are money ahead, most likely.
However, most ammo related problems will be minor, you can probably just fix it yourself easier. My new Rock River Arms rifle had a bad extractor, so I just swapped it from my spares kit. If you ever plan on relying on these rifles in a life and death situation, you'll want spare parts and the ability to fix the rifle yourself.