Is there any difference? is one "student" and the other "research paper"? I'm thinking they're pretty much the same thing.
While I am highly tempted to agree and while there may currently be significant and unnecessary overlap, I do not think those tags should be merged.
They should, however, be clearly defined.
[academic-writing] should be (IMO) defined as writing in the academic setting: A student with questions on utilizing multiple citations from a single source in MLA format, for instance.
[academic] should be (again, IMO) used for all other questions relating to the academic environment: A logic professor with questions on creating a home-brew textbook for his community college logic class, for instance.
I would consider the latter example relating to [academic]s, but not necessarily [academic-writing].