I was finally abble to make Gloox working with the JHB servlet.
The problem was a non-compatibility of JHB with the last XEP 0206
specifications (indeed the last code modification was 9 months ago!) .
I've posted a ticket about it on JHB, with a patch:
http://trac.jwchat.org/jhb/ticket/4
Hope this help!
Frederic.