While you may be disappointed that you can not queue as a DPS in DF it is possible to heal AND dps as a SCH. I find that with fairy heals and Adloquium it is relatively easy to get your DoTs up on a single target and spread them via bane. This may not be the case for boss fights but, as far as trash goes, SCH makes a good DPS/Heal slot.

Playing this way is fun and engaging, especially if your tank is geared and doesn't take too much damage.