The Shield SMSc co-witnesses with the iron sights on the Hellcat. So... after any/all windage adjustments are made the red dot should be directly over the front sight and the front sight should be 'centered' in the rear sight 'U' all at the same time. If any of those are out of alignment shot placement will be where the red dot is.
Try this. After you have placed the red dot, front sight, and rear sight together on a point move the red dot as far away from the front sight as you can while it remains visible in the window. Don't move the pistol. Keep the red dot on that point and move your head so that the front sight covers the red dot. Your rear sight will now be centered and you will have proven to yourself that shot placement will be where the red dot is and your iron sights have just shown you that. I think your real question may have been something like "is the red dot superimposed upon the front sight or does it rest on top to make an '8' of sorts?" ?
That's my experience and 2 cents. If I'm off maybe someone else here can help us both understand this better. Maybe with examples of how this differs with a red dot that does not co-witness with iron sights? In such a case could suppressor sights be used such that the end result would be co-witnessed?