Can I mount this to a sig sauer romeo zero reflex sight? — 2 Answers

Short answer - Yes!
Long answer: The holes of the sight line up perfctly with the studs and the threaded mounting holes on the mount. The pair of M4 screws that came with the Romeo Zero fit the best, rather than the ones supplied with the mount. However, the mount is about .175" wider and .3" longer than the sight. If you want the tightening knob on the mount to be on the left, the sight will mount flush with the back of the mount and the front of the sight will be set back .3" from the mount's front edge. The sight can also be flipped around and installed so that the knob is on the right. This will put the front of the sight flush with the front of the mount with the .3" offset at the rear.
Unfortunately, the shroud will not fit without modification. Two holes need to be drilled very near the front of the shroud to accommodate the studs on the mount. To locate where to drill. put a couple of layers of masking tape on the bottom front of the shroud. Line up the shroud's holes with two of the mount's studs and press the other two studs hard enough to make an impression in the tape. Carefully center punch, drill and file holes to fit.
With or without the shroud, offset to the front or rear, the Romeo Zero locks up rock solid and looks great any way you want to put them together.