Well, I am glad I tried this on a testing server before deleting my existing install - still a 500 error, this time with a *completely* fresh install, and again the only thing added is the Hueman theme.
Are there version checks I should make to MySQL or anything, or is there something in particular at which I might point my server support personnel?
If it helps, activating Hueman *totally* crashes the server; even the admin area throws a 500 error. This tends to suggest that there's something that is called by Hueman - probably custom settings submenu - when loading the administration page, that is also called when the "front" of the site loads.