According to Oracle you can indeed upgrade a WebLogic domain from 10.3.x to 12.1.2 but E1 Server Manager does NOT support an upgrade. The only way to have an Oracle WebLogic 12.1.2 E1 web server is to create it new. I am attempting to hack the server manager files around this but to no avail so far. If anyone else is able to upgrade successfully please let us know.
Here is the exact response from Oracle -
The developer says that there is no supported path for upgrading a JAS server
running on WebLogic Server 11g (10.3.5 or 10.3.6) to WebLogic Server 12c.
Such an upgrade path for JAS is not supported because development has never
tested and certified such an upgrade path for JAS.
The developer says that at some point you need to get on a supported
configuration for JAS. According to the developer, that means do the
following steps.
1. Install a new Server Manager agent to manage WebLogic Server 12c.
(You are not suppose to use the old agent for WebLogic Server 11g to
manage WebLogic Server 12c.)
2. Install a new set of JAS servers using the new Server Manager agent that
manages WebLogic Server 12c.
3. Eventually discard the old JAS servers and old Server Manager agent that
are using WebLogic 11g (10.3.5 or 10.3.6).
Also, I created knowledge document 1620352.1 to inform customers of this.
And I have attached a copy of the knowledge document for your reference.