A metatarsus adductus is defined as a forefoot that is adducted (medially deviated) on the rearfoot.
A clubfoot (talipes equino varus) is typically defined as a foot that is plantarflexed, inverted and adducted.
So with a metatarsus adductus the forefoot is adducted, and in a clubfoot the forefoot and whole foot is adducted, so yes they are related. A metatarsus adductus exists as part of a clubfoot.
Some consider a metatarsus adductus as just a very mild form of clubfoot and has the same cause as the clubfoot. While there is not 100% agreement of this, it does make sense.