[...] It's heard and used, but it's informal, slang, or just uneducated or illiterate. AHD did not have enough doubt about this to refer it to Usage Panel of writers, linguists, and other language commentators that it consults in questionable cases.
<intrepidly raising my hand>I'm sure all your fellow countrymen who routinely use snuck (including the ones who have answered in this thread) will be just thrilled to see themselves branded 'uneducated or illiterate', Æsop
I use snuck in casual speech without feeling self-conscious or lowering the register. It would be odd for anyone to consider me uneducated, let alone illiterate.
I suggest that the difference between "informal, slang" and "uneducated, illiterate" is great enough that the four terms shouldn't be used together to describe one usage.