As far as I understood it and people mentioned it - they do nothing illegal.

All the server code is freshly written and not from ea.

With your purchase of UO you buy your client and access to artwork and then just connect with your bought version of UO to their server.

The emulator server does not hold any artwork or any other licensed by ea and just provides information to the client.

As they are not making money with it and ea did not fight them from start (unlike wow does) I doubt they would have an easy time closing them down.

And for the fun I would like to see EA close down brazilian or russian servers.