It is generally accepted as gender neutral. Lately, I've seen a lot of LGBT communities encouraging its use.

Googling "Is dude gender neutral?" results in a lot of sites telling you that it is.

"In the early 1960s, dude became prominent in surfer culture as a synonym of guy or fella. The female equivalent was "dudette" or "dudess," but these have both fallen into disuse, and "dude" is now also used as a unisex term." Dude - Wikipedia https://en.wikipedia.org/wiki/Dude