they don't cast evil spells, and they don't breathe evil things, either.
Their "hunger for living flesh," as mentioned in their description, could be evil, but there's nothing in the code that supports it.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6841 c06c8d41-db1a-0410-9941-cceddc491573