Hair tends to grow faster in dreadlocks than normal hair in most cases. The reason for this seems to be the reduced amount of washing and stripping the natural oils from your hair and scalp. However, dreadlocks to appear to grow slower than normal hair because all that hair has to knot and tangle up to form the dreadlock.
So if your hair grows three times faster with dreadlocks yet it takes three times as much hair to knot up and form your dreadlock the appearance of length seems to be the same growth rate.