In my opinion, a mature non-breeding pet chin should not be fed a diet of an alfalfa-based pellet and alfalfa hay only. Their energy requirements are much lower and do not need the extra nutrients and calcium which is in alfalfa hay. This excess is what can cause kidney stones. However, a chin on a timothy hay-based pellet and loose timothy hay should also get a small amount of alfalfa hay in some form (loose, cubed). Like ticklechin mentioned, the chins on a timmy-only diet tend to lose condition... I have heard this from others who also fed a timmy-only diet at one point.
A breeding chin, pregnant or lactating female, or growing chin probably would not have any problems with alfalfa hay and alfy-based pellets. They need and utilize the extra nutrients. As a breeder, I use alfalfa/timothy cubes, loose timothy hay and an alfalfa-based pellet for all my chins and I also give my pregnant/nursing/growing chins alfalfa as well. My pet chins get the same with the exception of alfalfa which I only give occasionaly. I don't see any problem with giving a blend of timothy and alfalfa loose hay or cubes to any chin. I just think solely alfalfa hay as the roughage isn't appropriate for a mature pet-only chin.