You can set the points you get for killing zombies, but not currently the points for killing individual types e.g. Tank. What you could do is add this event to the spawn:
onZombieDeath -> Client -> incScore [5]
and then the killer would gain five more points than whatever you have set for killing zombies normally for the Tank. Alternately you could disable zombie kill points and use this event for all of them, setting points for individual types.