liverock only produces good amounts of ammonia during the initial period of adding it to a new tank. there is lots of dieoff at that time. or, if you get uncured live rock. then there is ample amounts of dieoff.
Also, overkill on nitrifying bacteria? not sure that can happen. Yes, it would take longer to cycle the tank. This is because a greater number of bactera need to become established. But I would rather have my bacteria die off due to not enough ammonia after i take out the shrimp and add my fish, rather than add a fish to a tank and have to wait for the bacteria to grow to get the tank back to a good balance.
With the shrimp, its easy to tell if your tank is ready. If you have a shrimp in the tank, and your ammonia levels are 0, that means that you have the bacteria and its cycling the amonia. If you take the shrimp out, how do you know you have enough bactera? A 0 reading may just mean that the small amount of bacteria consumed the amonia over time, but are still not established enough to handle the bioload of fish.
note : when referecing ammonia, this means nitrite and the bacteria for the nitrite as well.