Saw the video of the helicopter chopping off its own refueling probe. That made me wonder what the stall speed of the tanker is, and how difficult it is to fly slow enough for the helis to keep up.
The stall speed is around 95-100 knots for the older F variant, and something like 90-95 knots for the newer J variants.
A KC-130 can refuel between around 100 and 270 knots. The lower end of this is well within the maximum speed of many military helicopters, eg the Pave Hawk, Black Hawk, Chinoook or Sea Stallion.
That leaves an "overlap" of around 20-40 knots, without having to approach too close to either the stall speed of the KC-130 (around 90-95 knots) or the VNE of the helicopter (usually between 140 and 170 knots for a military helicopter). This is enough for aerial refuelling, which usually states a fairly tight bracket for the refuelling speed.
As mentioned here:
The United States Marine Corps has chosen the KC-130J tanker to replace its aging KC-130F tanker fleet. The new KC-130J offers increased utility and much needed improvement in mission performance. As a force multiplier, the J tanker is capable of refueling both fixed wing and rotary wing aircraft as well as conducting rapid ground refueling. The refueling speed envelope has been widened from 100 to 270 knots indicated airspeed, offering more capability and flexibility.