Although someone here might be able to help, this is not an official Webmin support forum. This is the Virtualmin forum, so it may help you to post on the Webmin official support forum as well.
Don’t recommend the SourceForge forum. We’re likely to disable it eventually. Nobody pays attention to it. The devs of Webmin are the same as the devs of Virtualmin, and this forum is much more active.
Nope. Same people. Jamie created Webmin in '97 and Usermin a couple years later (and I started working on Webmin within a year or so of its initial release; I had built my own web UI for products I was developing, but Webmin was better and much further along, so I dropped mine and started building modules and themes for Webmin). Jamie and I created Virtualmin and Cloudmin and founded the company together. Now, Ilia does a lot of work on all of them. There are several other volunteers, as well.
Oh, and to get back to the topic. I don’t know of anyone working on a GlusterFS module for Webmin. We aren’t.
I think it’d be a great fit for Cloudmin, but we just don’t have a lot of time. We’re too small of a team for too big of a userbase to take on big new projects. But…sometimes Jamie surprises us with some weekend project that would have taken anybody else months to produce, and filesystems are interesting to him, I think.