Several servers can be connect thru a hub, they can be in the same VPS or not although using the same machine is recommended, however multiple servers can never access the same world, a world is always attached to its main server.
Thank you for your reply.
Was thinking of these cause in some games (Not Minecraft) it's possible.
Cause they have the so-called "Channel System" and each Channel is connected to a different server.
Wouldn't it be cool if Minecraft have that "Channel System"?