You can have as many accounts as you like and trade items from one account to another if you like. Or having a group of friends jumping from server to server buying up mats and other stuff to trade with each other to craft cheaper or to just resell. It already exists in big style!
Also when you look at the Market Boards you can see the same crafter name on every server (at least on the Light Datacenter). I guess they do the same – and according to SE it's not against their TOS.

Like or not: according to SE it's not against their TOS but a game feature you can use, so more players should actually group up with their friends to buy and sell crafts and other stuff (bought from different servers within your datacenter), since SE directly encourages it.