Is it permissible to give Zakat al-Mal (obligatory charity on wealth) for feeding fasting people and providing for their sustenance, or for medical supplies necessary for treating the wounded? If so, under which of the eight categories of Zakat recipients does it fall? Or is it only supported by voluntary charity funds?

It is not permissible to use Zakat (definition) for breaking the fast of those who are fasting or for medical supplies, because Zakat is given into the ownership of its rightful recipient, and nothing should be bought with it on his behalf. Even according to the view that permits paying the value [in cash], there might be among those who are fasting some who are not eligible for Zakat. Furthermore, this does not fall under the category of "fi sabilillah (in the way of Allah)" according to the majority of scholars.