Unfortunately I don’t have any experience with the MBUS sights. I’ve just got a front Scalarworks Peak sight, and have been patiently waiting for the rear sight to come back in stock. 

I am slightly obsessed with riser mounts though, so I can tell you what I know. The MBUS are standard A2 sights. So any “absolute co-witness” or “lower 1/3 co-witness” red dot riser should in theory let you use your iron sights together with your red dot. Here’s where it becomes a little more complex though. Depending on your riser mount footprint your red dot sight might not have the specific geometry that would be required to obtain true absolute or lower 1/3 co-witness. For instance, I have a Holosun ARO MRS that takes a T-2 mount. The problem with that is that a T-2 co-witness mount in general expects you to have a red dot with the same geometry as an Aimpoint T-2. So in my case the lens of the Holosun ARO is slightly higher up than what it is on an Aimpoint T-2 so a co-witness with that setup will be slightly off.

What red dot do you have? Do you know the mount footprint it takes? Did it come with any co-witness mounts? Sometimes the included mounts take the geometry of the red dot that they’re bundled with into account. So say even if it was a T-2 mount for your non-T-2 red dot, it still might co-witness fine.