I'd be worried about parasites/bugs in the peat moss. Dust can be problematic as well.

As far as ingesting.. a snake's digestive juices can dissolve bones.. a bit of aspen shavings, bark, or newspaper isn't going to stand a chance in there.

Lots of people use aspen, repti bark, newspaper (I use it for all of mine.. it's free and so easy to clean out)