sorry for a late reply
opengrok just calls the elf binary of exuberant ctags and consumes it's output
I don't think this is a problem, since opengrok doesn't consume any code or links any library of exuberant ctags.
If this would be problem, then you could say that opengrok cannot be bundled with Debian, since it runs on kernel which is GPL and opengrok is CDDL ...
but I am no lawyer
I'll try to workout the integration scripts rather than fighting licenses ;)
also it seems
http://mentors.debian.net/debian/pool/contrib/o/opengrok/ needs to be updated to 0.7
thanks for comments
Lubos