I was testing last night and it seems that not all helicopters can see incoming missiles on their radar.

Helicopters that can see incoming missiles on Radar:
AH-99 Blackfoot (300 Flares) (Can also see when it is being acquired by AA and where from)
Mi-48 Kajman (192 Flares)
PO-30 Orca (180 Flares)

Helicopters that can't see incoming missiles on Radar:
AH-6 Pawnee (No Flares)
MH-6 Hummingbird (No Flares)
UH-80 Ghosthawk (180 Flares)
CH-49 Mohawk (180 Flares)