Millard Fillmore actually has quite a few examples. The page currently has 21 of them—Fillmore is known for being unknown. You can go by technicalities such as "they're just passing references and he doesn't actually appear as a character in the series", but normal tropes are also often just used in passing.
Wikipedia sometimes runs into a dilemma where (using a made up example) there are 12 ski resorts in an area and 10 of them are proven to be notable. It would be stupid to create 10 articles and leave the other two out.
If we are going to require that since presidents aren't works, they have to be notable, enough presidents are notable that we really should list all of them, even if they aren't all notable individually. There is no rule for this; it's just common sense.
As for Ron Paul, he's probably got a page because he's also a prominent libertarian and thus gets talked about on the Internet a lot by people who otherwise don't care much for the Republican party at all. I would be very surprised if the Ron Paul page didn't predate the Republican campaign.
I would agree that people like Arnie should only get creator pages with brief mentions of their political career. For someone like Reagan who can legitimately have full pages both as a politician referenced in the media and as a creator, I'd say to put it all on one page. Yes, you can make a separate Useful Notes page and creator page, but most people don't think that way and would expect a single page. Pick one to put the page on and have the other one redirect to it.
edited 29th Jun '12 5:18:03 PM by arromdee