The stucco will have to span between the valleys of the ribs, which with lathe (didn't mention this) a couple of inches should be fine. But over time I may be worried about waviness in your stucco since I don't think the steel sheeting has much in-plane stiffness (if we are talking about the type used on PEMBs)...
The other thing I would be concerned with is temperature expansion/contraction stresses of steel sheeting causing cracking in the stucco. If anything I would use densglass screwed to the ribs. This would somewhat isolate the densglass from the steel panels because the screws would yield/rotate slightly with expansive/contractive movements of the panels. Also it may help with your moisture barrier and temperature change issue in your wall section.
I've seen a lot of ugly stucco on plywood applications, moisture can wreak havoc on this system, so I would never recommend it. But maybe it works OK in dry climates, certainly is bad in Florida.
However, you may also be creating a moisture barrier/intrusion problem:
-Project location? Climate? More heat or AC?
-Type and usage of structure?
-Interior finish and insulation?
May also see what the Stucco Mfrs Association has to say about this type of installation...
Also a good one to bounce of some architect friends to see if they have heard of this and had issues with it.