Pretty sure that is just a general guideline. No way to actually test all possible configurations from the point of view of Oracle.
However you should certainly test your application on the targeted system.
> Does this mean that Java is not officially supported by Oracle with Windows
My view is that Oracle doesn't really "support" anything unless you have a service contract with them. Other than that if it works it works and if it doesn't good luck figuring out why.
Only Oracle support can answer a question about what is 'officially supported by Oracle'.
Did you notice on that page that 2008 R2 was certified. No one but Oracle knows the intention of certifying 2012 R2.