I have a DS Arms upper as well.
I just received my MBUS rear sight and installed it. my optic was already installed and zeroed.
when the rear sight is down, its flat and out of the way of the optic. flip it up, and take a sight picture through the peep hole, its nearly dead on to where my red dot is... I haven't fired it yet, but I'm going to assume that when I look through the peep, and take a normal sight picture with the front iron sight, and it all lines up with where my red dot is, that my iron sights are dang near zero.