Stealth helicopters do not exist to such a combat relevant RCS not to mention that you somehow think a helicopter can stay stealth when using ECM activaley which any 1960s old ADS will immidiatley catch on since you are emiting constantly electromagnetic waves.
NoE flights render most ADS systems operating in Pulse Doppler Radar regimes, useless or uneffective while low altitude radars mounted on high extractable masts like Russia and China use specifically designed to track low altitude flying aircrafts and Cruise Missiles with lowered RCS included will without doubt see anything as big and with the big RCS helicopters have due their design and the angles they have regardless if Stealth or not will reflect radar waves far better than LO Cruise Missiles.
If any country has the ability to track any kind of aircraft then it is the russians which have far more radars operating in different regimes as anyone else.
Further they are the only today operating combat relevant EMP vehicles.
Электромагнитное оружие: в чем российская армия опередила конкурентов - ВПК.name
Up to 300km EMP that can turn of any fine electronics.
Fact is that you clearly have no idea about US capabilities which were screwed with their "Air superiority" by little Serbia with 1970s technology. The entire Air campaign was rendered useless by tactics deployed by Serbians, almost no casualties among military and especially among SAM and ADS units, which the US after that started bombing civilians.