Actually if you are cycling a tank, there shouldnt be anything else in there unless you are cycling with uncured live rock. Ammonia is toxic to anything no matter how hardy something it, it will eventually die of suffer extremely bad gill damage since it would essentially be swimming in acid. Also the bacteria only grow to match the size of the available bioload, hence having 3 damsels will only produce a large enough bacteria colony to support 3 damsels, the only real advantage of this come from that Anerobic bacteria which break down Nitrates in low oxygen areas (which is what a DSB is used for) which always reproduce slower then Aerobic bacteria.
While there is no right or wrong way to cycle and aquarium, using a raw cocktail shimp will cost 1/10 the cost of a few Damsels, hence saving more money for other fish, also by the time the Cycle is done, the Damsel will have established a territory which it will aggressivly defend against all intruders, which would be any fish added after the cycle.