

I don’t work with merges, so maybe I’m way off base, but I thought they meant, they’re working on another branch or fork, then merging the base branch into theirs every so often to get the newest changes, and then that creates multiple merge commits, which they can’t squash at the end…?
I’m not sure, about that last part, but the rest, I’ve definitely seen with contributors that didn’t know to work with rebases (and unfortunately we’re on GitHub, which only half-assedly supports working with rebases by default).

You’re right that there is a risk, that rebasing introduces compile errors or even subtle breakages. The thing is, version control works best, if you keep the number of different versions to a minimum. That means merging back as soon as possible. And rebases simultaneously help with that, but also definitely work best when doing that.
There may be reasons why you cannot merge back quickly, typically organizational reasons why your devs can’t establish close-knit communication to avoid conflicts that way, or just not enough automation in testing. In that case, merges may be the right choice.
But I will always encourage folks to merge back as soon as possible, and if you can bring down the lifetime of feature branches (or ideally eliminate them entirely), then rebases are unlikely to introduces unintended changes and speed you up quite a bit.