Yes, it is entirely possible that the 2012 Wreck-It Ralph film exists in the Wreck-It Ralph universe, although admittedly it is never explicitly mentioned.
Unfortunately I don't think there is any single piece of hard evidence that proves it. However, I offer this conclusion based on solid reasoning that considers several well established in-universe ideas. I also considered the points you have made in your answer against the film existing in universe and I offer explanation of them as well, not as a slight against yourself, but simply to try and strengthen your belief in the possibility of the film existing.
Here is my reasoning:
We know that Ralph et al already know of a world outside
of their own; they are aware of the arcade, they know of the
players, and they know that these people are able to do things
that they themselves cannot (for example, unplug games). So the
idea of an unknown 3rd party making a film all about the life and
times of Wreck-It Ralph wouldn't be a completely alien concept to
them. They may still be surprised to find 'the players' are
interested enough in their lives to go to such lengths but it
still wouldn't be a huge revelation ala The Truman Show.
They have Wikipedia, Facebook and YouTube. Since Ralph et
al are new to the internet they probably aren't aware of this for
the duration of the film, but after just a little time exploring
on-line the concept of User Generated Content would be known to
them. It isn't clear from either film exactly how much 'the video
game characters' know about how much influence 'the players' have
over their world. They know it is based on 'the code' but do they
know that people outside of their world wrote the code? I'm not
sure. Opening their mind to User Generated Content gives them the
concept that 'the players' can generate stuff of their own. Knowing
this, I believe Ralph could then accept that a film of his
adventures could exist in universe.
Presuming the film universe is very much a mirror of our
own with a couple of fictional elements, it is probably safe to
assume they have Twitch. (For those that don't know Twitch is an
online streaming service geared towards sharing videos of people
playing video games (although it has started branching out into
other areas)). This would further back the idea of a film of Ralph's
adventures being possible, the idea that players have a way to
capture moments from their games to playback and view again later as
videos. Ok, this argument would need further 'finessing' to explain
how a game streaming service would capture out-of-game events, but a
simple explanation would be that those moments are in-universe CGI.
We have precedent from another Disney film! Toy Story! In
Toy Story the main character, Woody, is featured as the main
character in the in-universe TV show Woody's Roundup, yet he knows
nothing about it until told by another toy in the second film. Given
that Ralph et al live in a rather closed society (until the
introduction of the internet) it is perfectly reasonable to assume
no-one in their circle is aware of the film and hence it goes
unmentioned to him so he never knows about it.
Continuing to use Toy Story for my next thought (which addresses
your thoughts), in Toy Story no-one refers to Woody as the character
from the hit TV series, we (the viewer) don't even know he was in a
TV series until the sequel, and this is an in film,
series. You could argue that in the first film this in-universe show
hadn't been established so couldn't have been mentioned, but come the
third film it has been and yet still no-one mentions it. It is only
mentioned when they are actually talking about the show. So to me
the argument that no-one refers to him as the character from the
film doesn't really support the view that it doesn't exist, given
that the same thing happens here.
Even without the Toy Story precedent, if I was to mention to
you Ken and Ryu where are you more likely to know them from? The
1999 animated movie Street Fighter Alpha or the 1991 video game
Street Fighter 2? What about Mario and Luigi? The 1985 video game
Super Mario Bros or the 1993 adventure film Super Mario Bros? It's
not huge leap to assume 'the players' know and refer to Ralph as the
guy from the video game even when the film exists because that is
what he is best known for! Even further, perhaps in-universe the film tanked
and no-one knows about it other than the gamer geeks and nerds! I could
imagine why, consider how different the film is compared to the game
it is based on!
So in conclusion, yes, a film of Ralph's adventure could exist in universe. There is no strong evidence to suggest it cannot but plenty of circumstantial evidence to suggest it could.