I commonly see "snob someone off", where the word they should correctly use is snub.
Is using "snob" as a verb forever a no-no? Is it creeping towards accepted usage?
Snob does not appear as a verb in the OED1, Wiktionary, Dictionary.com, or Merriam Webster. Even Urban Dictionary doesn't seem to define it as a verb, but only as a noun. So I don't think it's "creeping towards accepted usage", unless it's doing so very, very slowly. (I don't hear either word enough to make a judgement based on personal experience.)
Is using "snob" as a verb forever a no-no?
No. The English language is constantly changing and in flux—just don't expect it to be commonly accepted usage soon.
1The OED has two definitions for "snob" as a verb, but they are both obsolete and are for completely different words that just happen to share the same spelling (but not etymology, definition, etc.).
The word should be snub, as noted by yourself. Snob and snub are two different words meaning two different meanings, and should not be confused with one another. There is no 'verbal' derivative for the noun snob. Although in today's society many words become used in new ways and are accepted(i.e. snob as a verb), nearly most of the time, it is grammatically incorrect.