Yes, the OEM version is a subset of the Enterprise version. The only difference between the 2 versions is that the OEM version only provides the new PDB database backend while the enterprise version delivers both the JE and the PDB database backends.
The OEM version is only available to our customers, and more specifically to our OEM customers that are redistributing it (although we do allow all customers to download).
I would recommend that you remain with the Enterprise version, you have no reason to use the OEM version.
Product Management Director - Directory Services / OpenDJ