Group plans usually can't disqualify for preexisting conditions, so it shouldn't matter if he is diagnosed.
I could never get insurance on my own, but getting it when I had a job was no problem. You typically are not required to disclose any medical information when you enroll in a company plan.
He needs to talk to the benefits handler at his job.
I think it depends on the quality of the insurance. My student insurance was a group plan I thought...and didn't ask anything about preexisting conditions. That is, until I used the insurance and then I had to prove prior coverage for things that were preexisting.
So yeah, more in the talk to HR camp.