You wouldn't need to use Desktop Redirector, even if you don't get BES. The Blackberry can check exchange mail using IMAP, if you allow IMAP connections. Basically, if you have Outlook Web Access, you can do it. When you're configuring the Blackberry email, just give it the Outlook Web Access settings.
This will only work for email though, not addresses and tasks and such. Does the user need that?