Let's assume they're using a Boeing Vertol 234, a civilian model of the Chinook commonly used for firefighting. They're double rotor, and as such the rotors are slower than most single rotor helicopters, at around 225 RPM [1] at full throttle.
The rotors on a chinook are 60ft in diameter [2]. This means that the edge of the blade is traveling about 188.5 ft per revolution. At 225 RPM, that's 706.8 feet per second, or ~481 miles per hour, on par with a commercial aircraft at cruising speed.
So yeah, smacking a drone into a relatively thin and lightweight rotor blade at over 400 miles an hour may cause a wee bit of damage.
[1] http://www.chinook-helicopter.com/standards/areas/blade.html [2] https://en.wikipedia.org/wiki/Boeing_CH-47_Chinook#Specifica...