Never write code you don't need to write.
Never deploy code you don't understand.
I completely customized an open 3d game engine because all of the others where slow and or complex.
So while I use other peoples Hardware and VM I don't use anything outside of the of the JDK that I don't have the source code and don't understand that is deployed.
The catch with jME for me was performance and platform support. It was to slow (that is not an issue on PCs) and does not support enough platforms (wanted Flash, HTML5, and J2ME as a possibility).