Units of PID for car' velocity?
Attaching units to them is odd to me, but sure, lets give it a crack.

Kp is the error in the velocity so is m/s
Ki is (setpoint - kp) * time, so still technically m/s * something, I would leave it unitless
kd would be acceleration as it is the rate of change in velocity so m/s/s

Confused how radians enter the discussion unless they are asking you to control the rotational velocity of the wheel which is not usually the same as vehicle velocity (they scale each other based on the radius of any turn the vehicle takes)

If so, 
kp' would be radians / second
kd' would be radians / second / second, 
And ki' is left with the same above, still radians / second with some odd scaling relation.