You could do a search, on google or on the forums. I've seen opinions ranging from "good for everything" to "dangerous, do not use." I strongly suspect the truth is somewhere in the middle!
Places that sell it do warn not to breathe it, so I easily believe that breathing it is a bad idea.
A google search turns up lots of page saying it doesn't work when wet, but does work again when dry.
Here's one example page:
https://www.pro-terra.com/hrf_faq/happens-de-gets-wet-will-still-work/
That would mean it's useless inside a chicken (wet). Underneath bedding may be wet or dry, and the chickens may or may not mix it up and throw it in the air when they scratch. I personally would just skip diatomaceous earth entirely, but as you've already seen, plenty of other view points exist!