Does cyradm display the password prompt? I did a fresh RedHat 8.0 + updates (Perl 5.8.0) install on a laptop so I could do some development while on the road, and the prompt for the password doesn't display. It took me a while before I realized that cyradm wasn't hung, its just silently waiting for input.
I get the same behavior with both Cyrus 2.1.12 and 2.2.0, so I know its not related to a change in Cyrus. What I don't know is if this is a problem with Perl 5.8.0, Redhat's packaging of it, or a problem in some library that Perl uses.
My system is a home-built (LFS based) kit, not RedHat. There is no pam, for example.
Anyway, if use
cyradm --auth PLAIN localhost imap
I do get a Password: prompt. I can type anything I want there, it doesn't matter. Then I get an IMAP Password: prompt. At that point I must type the actual user's password.
Then I'm in and it works fine.