I tried to verify this but couldn't find it. However, I did find that counter-hackers changed Morris' username from RTM to RTFM to get back at him [1], so I'm not sure he used the username 'rms'. Maybe the staffer got mixed up?

[1] Page 155: https://books.google.com/books?id=oLHMBK0iGkkC&pg=PA155&lpg=...