I found this:
Q. I want to have additional servers running Windows Server 2008 or Windows Server 2008 R2 in my SBS 2011 Standard domain. Do I need additional CALs to access those servers? A. No. As long as those servers are within the Windows Small Business Server 2011 Standard domain, your Windows Small Business Server 2011 CAL Suites grant you access rights to the other Windows Servers. Note however, the use of some functionality in Windows Server require additional licenses (e.g., Remote Desktop Services/Rights Management Services).
Here. I'm looking to find out if the CAL would also cover a Server 2012 or Server 2012 R2 member server of the SBS domain as well. Has anyone found anything from Microsoft one way or the other?
First, in regard to the CALs, SBS 2011 CALs no longer work for Server 2012 & R2, so you'd need to purchase CALs for them if you plan to go with 2012. The SBS 2011 CALs work for 2008 & R2 as you already found out, but the licensing model changed for 2012 and MS now requires CALs for any member server running it. This is the link for reference.
Now, as far as other features (like RDS services you referenced in your question, and other features too) you will need separate CALs for those. See my quote directly from the 2012 license page FAQ.
Let me know if you need further info.