IMHO (and don't take this the wrong way), this seems like high-order nitpickery. NaNo is rough-draft material, not take-it-to-the-publisher material. A line here, a line there... odds are it'll all sort out in revisions, and if it doesn't, your agent or editor will deal with it, as it seems to have no bearing on the actual plotline. (If your plot literally hinges on one passing comment, Something Isn't Right.) Holding yourself up over throwaway lines like this... it's how stories don't get written, drafts don't get finished, and dreams don't get pursued. Nitpicking leads to procrastination, which leads to giving up. And you haven't even written the first draft yet.
Seriously - come November, just let the words flow.
(Pertaining to the issue, I'm sure other people have thought of "vampirates" before, and will since. If you don't make it a key, recurring term in your story, using it once isn't likely to be a problem, but this is something you'll probably want to ask an editor or publisher or agent about. A lot depends on how long it takes for you to finish and market the story, and how popular the Vampirates series proves to be to invite comparison/potential Issues; I gotta say I really don't see it a lot at the library, not like I still see Harry Potter, so it may be a comparative flash in the pan.)