Yes the sites would still be 100% useable as the glass used in the Halo site is completely transparent. So long as the sites profile as you mention would not block the express sites base.

I would not do this to a classic and costly double but some, so long as transferring the site from rifle to rifle is not a concern, will mill a flat spot on the receiver and dovetail or pin the site into place making for a lower mounting profile, though you most likely would not need to on a 1/4 rib style express site.

The colt rendition is lower and flatter I belive then the one you showed with a much larger reticule around 50-60mm and is actually designed to use the iron sites through on colts rifles at longer ranges.

A picture of the c-more system with the rail mount you of course would not want to use.
http://www.andean-inc.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=TAOS&Product_Code=CMCRWODG-8

James F. Nixon III