The specs on the stepper motors I have say 200 steps/rev. I'm looking at the DQ860MA driver and it looks like the minimum steps/rev setting is 400. Will these work together?
They definitely will.
When your driver says "400 steps/rev" what they actually mean is : if your motor has 200 steps/rev, at this setting we'll be driving it at 1/2 microstepping, resulting in 1/400 steps/rev.
You typically want to drive your motor at at least 3200 steps/rev ( 1/16 microstepping ).
And that will be no problem at all for a 200 steps/rev driver, you can even go as high as 1/256 microstepping no problem.
Probably a good idea to look at the video here : http://smoothieware.org/stepper-motors