Back from my six stays at Radisson Group properties (5 x Radisson Blu, 1 art'otel; 4 x F&F rate, 2 x F&F discount) and was only asked for the F&F form at one of them (Bergen Radisson Blu). However, the person on the front desk in Bergen gave me the third degree about booking the F&F rate before typing a lot of stuff into the booking system.

So all up, while you're unlikely to be pinged if you don't have a form, there is a risk that they will do so. (Also, it may have helped I was travelling outside of peak tourist season...)