It is a myth that feeding in the enclosure causes aggression. If anything, moving them to feed them increases your chances of a bite because you are handling the snake while in feeding mode. Our collection is decent sized (35 breeding females, 16 breeding males, plus holdbacks and hatchlings...easily well over 100 animals when babies are hatching, sometimes closer to 200 depending on how quickly babies sell). Everybody eats in their enclosure, and nobody is aggressive. Even when we have live rodents in the room (we don't feed everybody on the same day, so sometimes we are cleaning enclosures, palpating, etc, while other snakes are eating). Typically, even our maternally incubating females are pretty mellow.
As far swallowing substrate, I have had zero problems, over a lot of feedings. The only time I can see this being an issue is if the feeder is wet.