I don't really know Guacamole, sorry. But there is a thread:
Haha there are no dumb questions.
I think both will work but you may try it with your existing Guacamole server first. I just found the link when googling about apache and guacamole. I thought you can use it to have the correct parameters when configuring the Nethserver apache reverse proxy module.
Same domain should not be needed. If your Nethserver is behind Untangle, you may port forward www to your Nethserver, which will reverse proxy to Guacamole.
But I do not know Guacamole, so maybe it needs some "special" configuration I don't know.