We are going to use Java on an Ubuntu 12.04 server, with up to date repositories. Does Oracle itself provide any (ppa) repositories, and is there any other stable and secure developers providing them?
Oracle does not provide PPA repositories.
I recommend using WepUpd8 installers repository, that download installations files from Oracle, asks for license agreement (once only) and installs all goodies including command alternatives. It is also very up-to-date.