They might want to know it exists, but it's not like they do code reviews.
I personally have a lot of small cruft on mine (old blog migration scripts), a commandline video downloader that has a few issues, ...
None of that code was done on company time, but most people I know and like to work with find a few hours on a Saturday from time to time to just hack up something.
So the good people who didn't are just SOL? I say this as someone who actually has crap published, albeit nothing complicated.
Furthermore, The "Github is your resume" crowd always claims they want to use it to see examples of how you code, meaning at least some of whatever you put there is supposed to be production-quality and representative of what you do or would write at your day job. They have a point, because otherwise Github is basically useless as a screening tool.
(same idea with a technical blog)
I just do all of my spikes and silly side projects in the open now. If someone is even interested enough to have a look I count that as a win.