ODAC OLE DB provider "OraOLEDB.Oracle" for linked server supplied inconsistent metadata for a column
Even though Oracle support note 207303.1 states that the 12c client works with 11gR2 client, this error seems to be caused by a compatibility issue between the 2 different versions.  To fix, I followed these steps: 


Uninstall the 12c ODAC version, by opening an Admin command prompt, changing directories to the installed Oracle home folder, and running: uninstall.bat all d:\oracle, where d:\oracle is my Oracle home location.
Remove the PATH environment variables
Reboot 
Install the 11.2.0.4 ODAC version "64-bit ODAC 11.2 Release 6 (11.2.0.4.0) Xcopy for Windows x64", download the "ODAC112040Xcopy_64bit.zip" option.  Make sure you install via Admin command prompt (the install command is: install.bat all d:\oracle11gr2 odac11gr2).  Download from: http://www.oracle.com/technetwork/database/windows/downloads/index-090165.html 
Add back the PATH environment variables for d:\oracle11gr2;d:\oracle11gr2\bin
Reboot again