It's dickish and karma will likely get them later on in the game, but it is also part of the risk you take in complying with a rebel's orders. On a server rule side, as long as they followed the RP rules we have for killing somebody, they can do that. From a server rule perspective, cops can even do that as well. Admins will not ban you for that, however if you are doing this on cop, senior APD will have something to say about it.