I hadn't heard of it causing rusting, but that it forces the lint back into the machine and it could cause problems. But it seems with your husband doing a thorough cleaning and oiling periodically, you probably won't need to worry about it.
One story about air in a can. I was using it to clean between the keys on my very dirty computer keyboard and after I'd finished, two keys were impossibly stuck -- wouldn't work at all. When I popped them off I discovered an accumulation of debris that apparently the canned air had forced together. I haven't used it since.