So the story goes, Wesley had, after some time exploring the universe with The Traveller, decided to go back and finish his Academy training after dropping out in his final year in the episode "Journey's End".
There's a deleted scene in Star Trek: Nemesis in which Wesley and Picard talk about how he's been posted on the USS Titan, so it's quite likely that he'd have to have finished the Academy and actually BE a Starfleet officer.
Then again, the Titan was Riker's ship, and Picard certainly let Wesley be a Bridge officer without graduating from the Academy, so, who knows, maybe Riker was similarly lenient :)
There is no way Wesley Crusher was getting to serve on a starship, after having dropped out of the Academy, without re-enrolling at the Academy to finish the curriculum and thereafter graduating. Riker letting him onto the Titan without having graduated defeats the whole purpose of having Starfleet Academy. Sorry if the ideas contained herein, or my method of expressing them enrages anyone ProfessorTrek 20:04, September 12, 2011 (UTC)
Thus, the response to this is that doing so is far from unprecedented. This is true; however, the Maquis from Star Trek: Voyager being integrated into Janeway's command in the officer hierarchy on Voyager was a special case. As Academy dropouts, Starfleet no longer had any responsibility for them; however, perhaps as Federation citizens but not Starfleet officers, Janeway deemed the Federation to still have a responsibility for them, because she concluded that Starfleet, as an agency of the Federation, had a duty to act in their best interests, but on behalf of the Federation, and not on behalf of Starfleet.
And, as nominal criminals, the Federation would have an interest in ultimately seeing to their punishment. And, Janeway felt they were smart enough to, and could be persuaded to be inclined to, lend a hand in a very extraordinary situation. Sorry if the ideas contained herein, or my method of expressing them, enrages anyone ProfessorTrek 20:08, September 12, 2011 (UTC)