Basically, in 2.4.3 they made it so the rocketbots are no longer able to be used in arena, but theres a simple way to bypass it. If you have a pet already out, (I used a firefly) and you spam click the Rocket bot it will start to cast and it will then be out for use in Arena. It's tested, and working etc, and I was using it in Rated Arena. (Note, for it to attack the player, the player has to attack YOU first.)
[Im not the author of this picture, credits goes to someone at mmoverload ]