sysadmin has ~300 questions and system-administration ~20
In my humble opinion the should be obliterated, and blacklisted. They seem like a meaningless meta-tag to me. If a question on SF isn't about system-administration/sysadmin then it is most likely off-topic.
I think we even discussed this before, and the consensus was to remove them, but nobody with the moderator access needed to do them all at once did it, but I can't find the post.
When these things come up, sometimes I go to SO to see if if I can find analogous situations. Then I try to think of a justification.
(trying to play devil's advocate here) It might be useful to divide all SO questions into at least one major category: coding, scripting, version-control, etc. Which could imply that SF questions should always belong to either server mgmt, desktop mgmt, network mgmt, documentation (applies to both), etc.
I suppose that would make me lean more toward a merge than eradication. Sysadmin is such a loaded and nonspecific term, I'd probably synonym it to system-administration, which is at least a (possibly) manageable definition. Provided we could all someday agree on whether a "system" is a desktop and/or server and/or network and/or any "group of independent but interrelated elements comprising a unified whole".
This is where the SO analogies break down. It feels like they actually have more self-defining terms upon which they can agree (a statement I'll guess they'd find pretty humorous).