When applying certain sound sets to units with certain model files, there is no sound responses altogether. 
For example if the Rifleman sound set is applied to all Night Elf melee units in the Editor the following will have no sound responses: Wisp, Faerie Dragon, Hippogryph (Unmounted), Chimaera, Mountain Giant, Glaive Thrower, Treant, Owl Scout (All levels), all buildings and all uprooted ancients.
However if I also change the model file of the aforementioned units to Rifleman they have sound again.
All of the aforementioned units/model files also seem to be able to play other sound sets of other units facing the same problem.
For example I can get a unit using the Chimaera or Moonwell model to play the Chicken or Skink (Neutral Passive) soundset, and incidentally the Skink and Chicken models have the same problem as the aforementioned Night Elf models as neither can play the Rifleman Soundset and a bunch of others.