Okay, so your config file section would be something like:
$rc_config['default_host'] = array('imap.server.com'=>'My Server',
'mail.server.com' => 'My Server 2');Of course, for each server you'd have to also define a specific SMTP server to use.
Now, if you're talking about a feature like Thunderbird (forgive me for not know OS X and Apple Mail) where in the left pane you have something like the following:
My Account| + Inbox
| + Sent
| + Drafts
| + Junk
|
Gmail| +Inbox
|
Some Other IMAP account| +Inbox
| +Drafts
| +Sent
Then no, RC doesn't have that functionality. I can't say whether it really ever will, but hey, it's been requested already