in my opinion the patch installer requires the SQL user and password for its session only because it can't use the user from db.properties due to not being able to decrypt the password. It can use any SQL user/pwd pair (windows or SQL) that has the appropriate rights to the database and everything that is necessary otherwise.
So to answer your first question, it may be all the same which account you specify (in the case of SQL mixed mode authentication) if both works. To answer your second question: it may not be important to use the same account (if both works).
/Funny because I never used a different user during ePO install/Patch install than the one I used in the /core/config page. However I can imagine that patch installer does modify the db.properties file with the user you give during patch installation./
I am interested in the background of your query, please share that with me/us if you don't mind.
Background of this q is I was applying patch ePo 4.6.5 over 4.6Patch 1 and used SQl credentials, everything wend smooth but at the end services were not started. and Wizard says "Wizard was interrupted before EPo installed completely. What could be reason?
I solved lot of EPO Installation or Upgrade issue(Wherein the installation wizard says "Wizard was interrupted before EPo installed completely.") and found that in most of the cases, ePolicy Orchestrator 4.x installation / patch upgrade checklist KB is not followed religiously.
Please go through KB71825 - ePolicy Orchestrator 4.x installation / patch upgrade checklist for known issues and see which step did you miss.
Also, for go through KB75766, to know SQL permissions required to install and use ePO
Please revert for any queries.
Q.2.Is it important to apply same account on ePO https://server:8443/core /config page which we intend to use while we apply patch and wizard askes you to provide sql user and credentials?
Ans. There is no hard and fast rule to use the same account on ePO https://server:8443/core /config page which you use while you apply while EPO Configuration.
The Account you are using should have the rights on EPO DB as mentioned in KB75766.
Please revert for any queries
let us take a look together into the logs, please attach here the %TEMP%\McAfeelogs content. You case suggests a rollback keeping occurring at or near the end.
Of course only after you have checked the list of prerequisites AJ has recommended and nevertheless your issue keeps occurring.