You may be overthinking it a bit, and that's a lot of letters and acronyms you're throwing around, there.
Decision altitude (DA) is just what it sounds like: it's the altitude at which one makes the decision and initiates the missed approach action. One may descend through a DA, and it's not uncommon to do so.
Non-precision approaches utilizing a minimum descent altitude (MDA) are hard altitudes; one can't descend below this altitude until the visual references necessary to continue are acquired.
On a precision approach with a constant, stabilized descent to the runway, establishment of a decision altitude makes sense. On a non-precision approach, or during a circling maneuver, on the other hand, establishing a hard minimum altitude also makes sense. It's best not to confuse the two. However, if one must do so, considering both as a hard altitude limitation isn't wrong, and won't get you into trouble.