The IDMS documentation on TCP/IP SUPPORT is at the following location:
Under the heading "Establishing TCP/IP Support" , "Prerequisites" is the following:
This section contains the prerequisites for setting up TCP/IP support in z/OS, z/VSE, and z/VM operating systems.
On z/OS, support for TCP/IP is implemented using UNIX System Services kernel functions. The userid assigned to central version should be granted access to these functions. Depending on your security environment, this might require defining an OMVS segment for the userid. For more information, refer to the appropriate security documentation.
So the resolution to the error
DC088070 Vnn T0 Error during TCP/IP initialization. ERRNO=12238, REASON=00000000
is as follows
The UID under which an IDMS CV runs must have OMVS access (as indicated by an OMVS 'Segment'), and that Segment must specify a valid (writeable) 'Home' directory.