the clear PS fluid is, in essence, the same base stock hydraulic oil that ATF is made from. The viscosity of both is so similar it allows them to be interchangeable in hyrdraulic systems outside of a transmission, of course. ATF just takes that same base stock, adds friction modifiers, seal conditioners, red dye, and specialized chemicals to maintain clutch life. The difference between specs(ATF+4, Dex, merc, WS, etc..) is the type, and amounts of these additives. This is how you end up with multispec fluids, where they find that certain additives, or more of them, have no effect on transmissions, so they can dope them up with all the different additives and call it multispec.
With the exception of the seal conditioners, a lack of the other parts will not cause any harm to a hydraulic pump system like a PS pump. Chrysler designs their PS systems to run ATF because its cheaper, and it helps the pumps last longer(though they never seem to). As long as you have mostly ATF4 in the system, the pump will receive the neccessary conditioners and will not have any problems.