I don't think the bukkit plugins move players to a different server, there's no support for that in the protocol (unless they had a corresponding counterpart plugin in the client that would make the switch, of course).
I believe the player already connects in the best possible route - that's what the routing tables are for; the player says "connect to IP A" and that's it. There's no way in TCP/IP to say "connect to IP A through router B and then router C"; only the router config does that.
Easy to see - grab some advanced networking tool - wireshark or maybe even netstat would do; connect to such a server, note the connection IP, then move to a different world, see if the IP changes. I'd be very surprised if it did.
I believe the player already connects in the best possible route - that's what the routing tables are for; the player says "connect to IP A" and that's it. There's no way in TCP/IP to say "connect to IP A through router B and then router C"; only the router config does that.
Easy to see - grab some advanced networking tool - wireshark or maybe even netstat would do; connect to such a server, note the connection IP, then move to a different world, see if the IP changes. I'd be very surprised if it did.