Cookie sheet in the oven. 250° for 20 minutes. That's the temp I use for wood or rock items. Not sure but it might be too high for leaves. Might be best to lower it and monitor it while in the oven.
Just an idea.

I think treated it's fine to use as an addition to substrate. I do think it would trap and hold moister/feces and make it hard to spot clean.
Just my opinion.