Is RDPlus compatible with SBS Windows operating systems?

Yes, RDPlus works fine on SBS 2012. The only detail you should be aware is the requirement to change the RDPlus web servers (HTTP/HTTPS) port numbers to avoid a conflict with IIS.
You can use the AdminTool to change it to 8080 and 4430.
 Check this << FAQ >> for more detailed information on how to change RDPWeb TCP port.