As far as I can tell, Alfalfa and Timothy hay are fine for dragons, the fresher it is the better though, as the vitamines in hay fade relatively fast (more than 50% gone in 6 months). I wouldn't recommend it as a stable, as collard greens etc have more calcium than hay does, but don't see why it can't be mixed in with other dark leafy greens. Also, should use the leaves more than the stems, as hay (timothy and alfalfa) can have very woody stems.
Alfalfa sprouts are good too but don't contain as much calcium as the older plant but do have a fairly high water content so work great as a topping to the dragon's salad.
I have checked several of my bearded dragon books and Alfalfa sprouts and hay and Timothy hay have been listed as good foods for dragons. If there is any more up to date information on why hay should not be fed to dragons, certainly would love to hear it.