This is exactly what I did, mainly because I couldn't find one single sump that was big enough for what I wanted to do. I got an Eshopps 30" sump and an Eshopps 30" refugium and tied them together with 2 bulkheads.
I thought it was a great idea, and honestly thought of it myself.
My returns run to the middle. Sump with filter sock and skimmer runs to the left, refugium runs to the right, and returns run straight up to the tank. Plenty of room for equipment and future upgrades.
Yesterday during a storm, electricity went on and off for a bit, after this only one pump came back on, but tank still filtered. This was also a reason I wanted 2 pumps. Water level in sump ran higher but doesn't overflow because they are joined.
Mine has been up for 16 months without a hitch, I love the way it came out.