Wyatt,
We were in your situation over a year ago… all Final Cut/X-SAN, and switched to AVID/ISIS. We did NOT get rid of the X-SAN and still use it for archiving, storage, and the occasional FCP project. We added the ISIS and storage into the mix. Here’s what we did.
We left in place all of the dual ethernet cabling and fibre from the X-SAN install. In our server rooms, the ethernet terminates into patch panels. When we did the Avid/ISIS install, we added new cisco switches to conform to the ISIS specs. Our IT network has the ethernet organized into domains, so for example the XSAN had two separate domains, one for metadata and one for internet access. We simply added a third domain for the ISIS, and now depending on which NLE you want, we can plug the computer into one of three domains.
To answer your original question: NO… you shouldn’t run everything on one domain.
It’s kind of like that scene in Ghostbusters… you don’t want to “cross the streams” or who knows what kind of havoc will ensue! Hope this helps.
mark