I think that depends on your base-Installation of OBIEE and also WebLogic. What are you using right now?
Edit: As you can see in the Certification Matrix (Doc ID 1109260.1 ) OBIEE 184.108.40.206 is compatible with WebLogic 10.3.5 (and it is not necessary to update your WebLogic to Version 10.3.6).
Nope. Unnecessary unless you need 10.3.6-specific functionality. 220.127.116.11 out-of-the-box still comes with 10.3.5 so you're more than fine staying on that level - unless: see phrase one :-)
It is not necessary to upgrade to weblogic because he has told "IF we need to install the ODI, we Need to upgrade the weblogic 10.5 to 10.6,
In the same weblogic Domain, we need to Extend the web logic Domain for installing the ODI as ODI is compatible with the 10.6 version we need to upgrade to 10.6
It is just for ODI IF you want to install ODI then an then only you need to upgrade because ODI is compatible with the 10.6 version.
If you need BI Apps, then you need to upgrade, yes. My comment was pertaining to pure WLS functionality in an OBIEE context since this is the OBIEE forum and not the OBIA forum.