I posted this a while back, but have only recently fully determined the issue.
It looks like openfire’'s internal DNS does not work for services running on “sub-subdomains”.
EG, if I have hosts AAA.BBB.CCC.COM and XXX.YYY.ZZZ.COM, with the former running a conference service, to enable
XXX.YYY.ZZZ.COM to be able to browse the conference service on AAA.BBB.CCC.COM, I need to add:
XX.XX.XX.XX conference.AAA.BBB.CCC.COM
to /etc/hosts on XXX.YYY.ZZZ.COM (where XX.XX.XX.XX is the IP of AAA.BBB.CCC.COM).