When I fired up oXygen for the first time after upgrading from Mac OS X 10.8 to 10.9 (Mavericks), the system prompted me to install Java 6, even though I had already installed the Java 1.7.0_45 JDK from Oracle:
To open "Oxygen XML Editor," you need a Java SE 6 runtime. Would you like to install one now? Not now / Install
I had thought that Oxygen was bundled with its own JRE, and expected that at worst it would fall back on the system version of Java.
I don't consider the Java 6 requirement a problem - just a hiccup. Posting here in case others encounter this.