As per http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6550137, java.util.zip doesn't support symlinks. Since RHQ uses those classes for handling the contents of bundles, it does not support symlinks inside bundles. A use case for when you may want to do this is installing the EAP 5.1.2 RHEL native components via a bundle. As of 5.1.2, the zip from the customer portal contains symlinks to some OS-provides shared libraries, rather than copies of them. This is not likely to be easy to fix, without moving to a different archive-handling libraru, and I'm not certain ant supports symlinks in zip files either.
A work-around is to put the symlinks (and optionally other files) into a tarball and extract them using the ant script: <untar src="abc.tar.gz" compression="gzip" dest="somedirectory"/>