I don't think they should be merged. They overlap, but unprofessional-behavior is mostly about dealing with unprofessional behavior. Implicitly, presumably the OP would like to deal with the unprofessional behavior in a professional way, but that's vacuous as any poster wants to handle any problem in the workplace in a professional way.
Professionalism is a good tag but barely, for exactly the above reason: it's an implicit issue in so many questions. I would definitely not expunge a specific tag in favor of a general one that may even get too big.
The unprofessional-behavior seems to be used correctly (at least by way of my understanding) for most questions. Some questions of varying quality to which the tag is applied:
The first and third are about behavior that is definitely unprofessional and has occurred. This is a good use of the tag.
The second was closed because it's actually a legal question, but let's go with it for now. The question is about behavior that the OP feels is probably unprofessional but they have questions about it anyway. If the tag were replaced with a hypothetical transporation-issues the question, based on title and tags, would actually be different: perhaps the OP feels sleeping in the office is perfectly professional but wonders if other logistical issues will arise.
The tag adds meaning and value. The title itself could use some work, but that only makes good tagging for novice title-writers all the more valuable.
So the tag makes sense and is adding value. It is used correctly often enough, IMO not too differently from other tags or for the relative question quality within the tag. The tag is more specific than the rather large professionalism tag. I think this is a strong case for keeping it.