I suppose if they squashed commits that weren't there's, then that's a problem of course. But just rebasing their own work between branches?
The real trouble I'd see for this mythical newbie is when they get in a situation that calls (correctly) for a force push. That would come-up if they fork an OSS repo, push some changes to their fork, then do a $ git pull --rebase from the OSS repo to bring in new changes.
When they go to push again to their fork, they will get an error that will require a force push. The force push will be fine because they are working alone, but it could cause an issue for a new git user.
But I'm a little unsure of what trouble you're afraid the maintainer would have.