Time to necro. I looked into this a bit more, and found
this post about how it's supposed to work: "This allows wings or commanders in multi-crew to engage in exploration together, each earning credits and exploration rank and making the process more efficient."
So it's definitely bugged, and not working as intended. Crew members ought to get credits and rank progression, but no tags. (Which makes perfect sense.)
I posted this again because of the new system, if somebody could confirm that the bug still exists, that would be great. See the issue
here.
Personally, I'd love to open my ship for exploration multicrew, so that system scans would take much less time. (It would also provide a nice bonus to ships with two crew seats available.) But understandably, whenever I warn people that they won't get anything for helping, they pretty much always leave. Can't say I blame them, either.