Happy to oblige! If you go by Don Rosa's series only, then Mickey, Goofy and crew are not part of the Duck universe (but then, he doesn't particularly like Mickey).
He did at one point plan, and do a basic script and sketches to, a story where Mickey and Goofy did appear, but this story treated Mickey as a famous movie star whom Donald spent the entire story trying to get the autoograph of. They only met on the very last page, after Donald, victim of a huge slapstick sequence, collapses on the street and Mickey comes by and helps him up. The twist is that Donald doesn't believe that this is the famous Mickey Mouse, because "everybody knows Mickey is a tall, good-looking guy."
Disney didn't like the idea, so the story was never published.
If you move away from Don Rosa's story only, though, the official stanze on it is that Mickey and Donald do indeed exist in the same universe, even though their stories and lives are mostly kept separate, and they do cross over occasionally -- according to several European-made (and translated) official publications, Mickey, Goofy et al. even live in Duckburg (just in another part of the city, which is why they don't meet up with the Ducks too often). The American publications tend to treat them as living in different cities and having to travel a bit in order to meet up, but personally I like the idea of having Mickey and Goofy live in Duckburg.
As for Chip an' Dale, they have been in many comics and clashed with Donald several times in the past (although the chipmunks tended to be less sadistic in the comics than they were in the cartoons), but I haven't seen them in comics for years now... they seem to have been phased out with the introduction of the Chip'n'Dale Rescue Rangers cartoon, which portrays them in a completely different situation, and it looks like they've just stayed mostly away from the comics even after the cartoon series ended.