Below another active question about setting up a database for KiCad:
From what I understand, you have to do a bit of programming or make some setup files to interface KiCad with the external database, and as a result KiCad is not even aware of what database back end is being use. It is only aware of the interface. I guess this means you can use any database back end, and real time syncing either over a LAN or the internet.