As long as you have the same information on all servers, this should not be a problem. It gets to be a problem if you have the same agent paused on server A and not on server B.
About logging in, as QM calls Asterisk dialplan to do stuff, you could intercept the call and make it log in to other servers as well (you could Dial a special extension on the second server to log iin)
My suggestion is to run a test using a clustered demo key, so you can find any problems before committing to the solution.