[Oh]

You can use any username in any server, say Johnny was playing in a stunting server under the name Johnny and Chad went to Freeroam, he could use the name Johnny on that server. The accounts depend on what server you go in, if the username is available on that server.

So you could use "Alex" in some servers that don't have the username "Alex" registered, and some of the servers you can't because the username "Alex" would be taken. You just never know.