Yes you do.
I contacted Matt Gerber at ENS Group in Fort Wayne, IN and confirmed it with this email from Matt:
RMS Licensing Basics
To use RMS, organizations need the following licenses:
· Windows Server 2008 R2 Server License
· Windows Server 2008 Client Access Licenses (Windows Server CALs)
· Windows Rights Management Services 2008 Client Access Licenses (RMS CALs)
A Windows Server 2008 R2 Server License is required, since RMS is a component of Windows Server. A Windows Server 2008 CAL is required for every user who accesses or uses the server software. In addition, every user who creates or views rights-protected information through Rights Management Services requires an RMS User CAL. As an alternative to User CALs, customers may acquire RMS Device CALs for the devices used to create or view rights-protected content. Both user and device CAL options are available for RMS and Windows Server 2008.
In addition, organizations have the option to acquire an RMS 2008 External Connector (EC) license. The RMS EC license gives organizations the right to permit an unlimited number of external users to access or use a single, licensed copy of the RMS server software without the need to acquire CALs for each external user. The EC is an alternative to CALs when, for example, an organization creates rights-protected information or documents and needs to allow customers or business partners to view this information. Each copy of RMS server software being used by external users requires its own EC license.
Since external users must also be licensed to access Windows Server 2008 R2, the Windows Server 2008 EC license may be used as an alternative to Windows Server 2008 CALs.
But this link gives more details: