Not sure what happened to that link, but I as far as I know it should make absolutely no difference for security purposes if one chooses the latest Java 7 update or the the latest Java 6 update. I would guess both code lines are patched to same level.
Perhaps you are referring to recent press about vulnerabilities in Java 7 updates _06 and _07? Those issues only apply to browser plug-ins, totally unrelated to SQL Developer, and those can be disabled easily without removing Java.
The official recommendation is to use the latest Java 6 update (jdk1.6.0-35) for SQL Developer. We recommend avoiding Java 7 due to bugs, but bugs unrelated to security.