In my experience the fouling is much the same on a half tide mooring as it is on a deep water one. Barnacles in particular are intertidal animals, and may actually prefer a drying mooring. Obviously it will vary with locations, but one thing to remember is that mud will partly coat the antifouling, and may inhibit its working.
My experience of 20 years + in a drying marina with soft mud is that the hull as a whole is generally better, depending on the antifouling used, than those permanently afloat but the belly of the boat that sits in the mud is very prone to barnacles as the mud seems to rapidly make the antifouling ineffective. One other point is that where the rudder rises and falls in the mud most antifoulings rapidly erode. This is not too much of a problem unless you spend a long time permanently afloat after this has occurred