It's not against any rules however you're technically limited on what you can do. I think the best you can do is make the player vitals look like a signature mob. You can't mod the eye and flame graphics or add them to the player vitals.
Take a look at this file in the
V3B2 art pack.
opponent_vitals_backdrop_elitemaster_mp.tga
Try using that graphic in place of this one:
player_vitals_backdrop.tga