We have an attached daycare, and the cost is cheaper for employees. Definitely a selling point for physicians, nurses, etc. The key point that may be different from other daycares, though, are the hours. To really make it work, the drop-off/pick-up times have to match the standard shift times.
I don't know all the details, but from my experience I think a question would be whether you run the daycare vs. contracting some existing third party to open a center (either in the hospital or nearby).