I did the upgrade to 8.1 64bit Desktop and Server and am subsequently having issues with my Oracle connections.
If i dont get any ideas from the forum today then i will follow up with a support case tomorrow.
All i can suggest for you is to try 8.1 desktop - both 8.0 and 8.1 desktop can be installed side by side without impacting each other. Try to make a connection to Oracle and see if you encounter any issues.
You will need to download a the new driver--especially, if you are using Tableau 64-bit version.