You might find this useful:
http://java.sun.com/sfaq/#otherBytes :
Frequently Asked Questions - Java Security
17.If other languages are compiled to Java bytecodes,
how does that affect the applet security model?
The verifier is independent of Sun's reference implementation
of the Java compiler and the high-level specification of the
Java language. It verifies bytecodes generated by other Java
compilers. It also verifies bytecodes generated by compiling
other languages into the bytecode format. Bytecodes imported
over the net that pass the verifier can be trusted to run on
the Java virtual machine. In order to pass the verifier,
bytecodes have to conform to the strict typing, the object
signatures, the class file format, and the predictability of
the runtime stack that are all defined by the Java language
implementation.