Absolutely!....and a strong, overpowered one at that. With bacterial driven systems, there is constant die-off of bacteria due to its short life span. A strong skimmer is key to removing the dead matter before it starts to decay. It is actually recommended that you run the outlet of your reactor to a spot right in front of the skimmer intake. An inefficient skimmer with a bacterial driven system will almost certainly result in a crash at some point...most likely from ammonia at the start of the nitrogen cycle.
Here's an excellent article on probiotics, primarily Vodka dosing, but it touches on pellets as well:
Edited by jcom - October 21 2010 at 2:01pm