It's been pretty well established that needlessly (male) gendered language makes people feel excluded. Actually, that's too nice. That kind of language excludes people. Period.
It communicates that the speaker does not contemplate a non-male audience. I do not know about the communities that you moderate, but constantly assuming a male audience at a place like 18F is wrong factually and is disrespectful.
I've triggered the slackbot by using "guys" many times and I've never felt that this was aggressive in any way. It's usually a chuckle-worthy experience for all involved. And that's why I love the bot. I do understand concerns over "policing" language. No one wants to feel pestered into writing/talking in a way that feels unnatural to them. However, instincts should not be above criticism. And a silly bot[0] is a great way to gently, politely, and humorously help people unlearn behavior that excludes.
[0] We have other silly bots, too. The one we probably love to hate the most is angrytock (https://github.com/18f/angrytock), which will remind us to submit our time cards (using our open source time tracker, Tock. https://github.com/18f/tock).