Read the first sentence of the OP, please, folks.
Forget it Islidur, it’s Doperville.
Captain Kirk et al met Abraham Lincoln, and possibly members of the Clanton/McLaury gang on alien planets, which aren’t really alternate history…
Uhtred seems to make enemies with the pretty big majority of the Christians with whom he has dealings… I find rather delightful, Cornwell’s having him stubbornly sticking with the old religion of the Norse gods, at a time when militant Christianity is greatly in the ascendant in Britain – he certainly doesn’t make things easy for himself.
In the Dancing Gods series the protagonists at one point visit an evil magical kingdom ruled over by someone known as “The King of Horror”. When they meet him, it turns out the King of Horror is Stephen King. “Where do you think I get my ideas?”
The Defenders from Marvel Comics appeared on the David Letterman show in-universe. Letterman got to bonk a supervillain on the head.
In the Time Wars series the protagonists meet a number of famous people. One I recall was when they ran into Jules Verne, who caused problems when he figured out that they were time travelers. Then he also with them was captured and taken aboard a submarine captained by a fanatic…you might say Verne got some inspiration fuel.
Time travel fiction in general has plenty of that sort of thing.
President Obama met Spider-Man once: http://comicseater.o.c.f.unblog.fr/files/2012/11/baracomics1.jpg
Dickens’s Mr. Turveydrop in Bleak House talks about having met the Prince Regent (or at least having been noticed by him) but the encounter isn’t actually shown.
There are gazillions of British fictional characters who get presented to the current monarch(s) at court, such as Mrs. Poppit in E. F. Benson’s Miss Mapp.
Actually, I think it’s more difficult to come up with examples of a realistic novel that has absolutely no fictional character ever crossing paths with a real-life famous person.
In The In-Laws, John F. Kennedy apparently summed things up for Vince Ricardo with a quick “Well, At Least We Tried.”
Are you interested in joining? The benefits are terrific. The trick is not to get killed. That’s really the key to the benefit program.
Der Trihs:
I don’t think he means that he actually met Sullivan, but that he learned through some sort of Sullivan correspondence course, like the Charles Atlas body-building ones from comic book ads.
The Obama example doesn’t seem to follow what you’re going for. Spidey doesn’t name drop meeting Obama nor do we see a newspaper cover of the two meeting one another or something similar- we actually see the two meeting. That’s the comic version of something like Granny meeting John Wayne.
Lots of comic examples:
I’m sticking with my examples of Curb Your Enthusiasm, Don’t Trust the B---- in Apartment 23, Mike Tyson Mysteries, and Seinfeld. You can also add Arrested Development (Carl Weathers), Episodes (Matt LeBlanc), Louie (Louis C.K.), and The Sarah Silverman Program (Sarah Silverman and Laura Silverman). Those shows all depict fictional characters meeting an actual life famous person.
Why? The OP states the following doesn’t count:
“famous people doing cameos in movies or TV shows (like Stephen Hawking’s appearances on The Big Bang Theory)”
In the 1970s, Captain America punched a masked villain who was strongly implied to be Richard Nixon.
And Nixon, as well as many others, show up as living heads in a jar, on Futurama.
Maybe I misunderstood. Are you saying that your examples include instances where someone like Jerry Seinfeld mentions meeting a famous person (or it happens in some other way but isn’t actually shown)? You didn’t tell us who the famous person is in Seinfeld or in any other of your examples. If the meeting is actually shown, the OP is stated it doesn’t count (except in comics 
).
In Star Trek: Voyager, the crew met Amelia Earhart, I think.
Yes, and she was played by an actress. See OP.
Might as well see this too:
https://boards.straightdope.com/sdmb/showthread.php?t=868590
Ah, got’cha.
How about when the Ocean’s crew met Bruce Willis, and mistook Julia Roberts’ character for the actual Julia Roberts?
Cameo.
Mistaken identity in the Ocean’s universe- Roberts was playing a character, not herself.