In order for nitrifiers to colonize in great numbers, certain criteria must first be met. 1) Must have a flow of water high in dissolved oxygen. 2) Must have a constant food source... ammonia/nitrite. 3) Must have a suitable media to colonize (gravel, sponge, any other bio media).
Since nitrifiers are not free-floating/swimming, we can rule out that water would be a suitable media. Thus, they are not found in great numbers in water.
So unless you have an undergravel filter which basically draws a current through the gravel to satisfy these 3 criteria, nitrifiers only occur near the surface of the gravel bed. This holds true for any surface in the tank (glass walls, ornaments, driftwood, plants, etc.). These places will have a certain number of nitrifiers colonize because water flows through them... lack of which would encourage anaerobic activity.
That being said, the ideal place for nitrifiers to reside is in your filter bed. That's where the majority of your nitrifiers will colonize because it satisfies all 3 criteria (oxygen, food, and media). So basically, you can cycle a new tank (with a minor stumble in your ammonia/nitrite readings) if you use a seasoned filter. The minor stumble is caused by: 1) water parameters can never be exactly the same as the old tank water, thus nitrifiers would need to adjust. 2) you are still missing nitrifiers that were present in the old tank's glass walls, gravel, ornaments, etc.
Short answer to sum up this long rant... you CAN use a seasoned filter to significantly reduce cycling time. Just make sure to not overfeed and overstock your tank so the nitrifiers can keep up.
