I just learned how to do this from a fellow Forum member and wanted to post it up here in case other do a "search" for this. Very few are aware you can do this, or that Droid/Eris allow you to do it at all.
- Open Exchange email client
- Select Menu>>Compose
- Select Menu>>Add Recipient
- Select To
- Select Company Directory
- Begin typing in a name or distribution list that lives on the server Global Address List
- Select the name
- Compose your email