I am conducting some camera & lens tests and would like to hold the shutter speed at a constant and vary the exposure over an approximate 5 stop range of apertures. I'd like then to correct the exposures as closely as possible in ACR. Are the values shown for the exposure slider in stops or something other? In the end with respect to exposure, contrast and brightness I would like all of the images to very similar without repect to sharpness.
The Exposure slider is indeed in stops (-4 to +4 EVs) but you will find that it isn't completely equivalent to changing the exposure in the camera due to other settings in ACR also coming into play, although you may be able to find a set of brightness/contrast/black-point/toning-curve/camera-calibration that come close.
Yes it'll be in stops as long as you're moving in the positive direction (e.g., Exposure = +1, +2, +3, +4).
The negative direction is different (and is not well defined in any case because there is nothing available above the clip point).