When building an uberjar with one-jar, I always get these lines printed out:

NOTE: /alpha/bootstrap/onejar/src/com/simontuffs/onejar/JarClassLoader.java, line -1: Some input files use unchecked or unsafe operations.

NOTE: /alpha/bootstrap/onejar/src/com/simontuffs/onejar/JarClassLoader.java, line -1: Recompile with -Xlint:unchecked for details.

I don't think so. I haven't tried though.