I have now got a reply from the dealer - the 1.2 4x4 now uses an electronic 4x4 system (and not the old viscous differential) which does work in conjunction with esp.
Fiat's website still talks of viscous coupling, but they stopped using it at least 18 months ago. Cross's have had issues with solenoids failing (wasn't there even a recall?). But assume replacement parts last longer.