Can a Mac Mini, Server edition, be booted off either of its two disks?
I'm interested in having one disk with OSX Server on it, and the other a dual boot Linux/Windows, to get around OSX's fussiness about boot loaders.
Yes.
For OSX just install again on the other disk then System Preferences-> Startup disk will offer a choice.
For Windows install via BootCamp and the Windows disk wiull show in the startup volumes.
For Linux you might have to look at rEFIt