From a quick survey, it looks to me like the tags are used mostly interchangeably, but not always.
Of the 11 questions tagged with job:
It seems to me that many of the questions tagged with job are mis-tagged (they should have work-environment instead), but that in rare cases work-environment is not appropriate even though questions are related to jobs or professionalism in some way.
I don't know that we should declare that the tags are synonymous (there are at least some cases where job is used and work-environment doesn't quite fit), but job is being used vaguely as a catch-all.
I'm not sure that job is used in a sufficiently consistent way that we can or should attach guidance based on how it's been used so far (for the cases which don't overlap with work-environment), but we can be more prescriptive about how the tag is defined.
So, I'll agree with your second suggestion: we should add tag guidance to job (and all tags, probably, should have some guidance attached). Otherwise we should consider removing the tag altogether.