It's available to everyone, but it's a crapshoot as to whether or not you'll even get high/fever since you can't guarantee the same players are going to be getting kills all time (Though the chances are obviously higher on burst heavy classes like DNC/BLM) unless you're in a premade or something which makes it inherently flawed as a balancing mechanic.

What practically amounts to luck can make the difference between an evenly matched team ending up with no highs/fever or multiple fevers.