There is really nothing wrong with someone telling someone else "here is some cash, if you want it though, you have to pass a drug test". I wouldnt even mind making sure they are not using alcohol, as well. And it does sound like it is minimally cost effective. According to the reports, it will save around 50,000 dollars per year, total savings for the whole program, net.
However, as a liberal, I'd want to offer addicts treatment. I think this would also be cost effective, from the standpoint of the economy. Fewer intoxication related driving accidents, becoming a contributing member of the economy, and so forth. Of course, that last part assumes there are the same number of jobs in our economy as there are workers who want them, which right now is not the case.