I don't see any options to use conditional tags in the
glossary. However, you can exclude the entire glossary by creating
a single source layout with the Glossary option unchecked (and call
the output "NoGlossary," for example). You can create a second
layout with the Glossary box checked, or just use this as the
standard layout/output.
With conditional build tags, you would have to generate
outputs to different directory locations. Different single source
layouts require the same if you don't want one to overwrite the
files of the other. In this case, one directory for the help with
the glossary and one directory for the help without.
No idea if conditional glossary tags will be a feature of RH
7.
Hope this helps,
Ben