IMO it's going to be the Wizard as he'll see them as yet another being that he can commune with and eventually attempt to control yet inevitably fail, just like the Junimos, his ex-Wife, and the Farmer. The difference this time is the Junimos already knew he tasted bad, the ex-Wife already knew his taste in interior decoration was bad, and the Farmer knows his squirrel-nut ridden "Forest" stew tastes awful.
But the zombies don't know how his brains taste and sadly will never know as they've expired and gone right off.
And anyway, who do you think is commanding the zombie rebellion? Why are they invading Pelican Town in the first place? If the landing party is arriving in early game, they'll find a shortage of brain salads as the Farmer hasn't unlocked Personality 1.0 or Socialization 0.9 beta on quite a few of the townies yet. There'll be quite a few disappointed undead tea parties had with the Mummies in Skull Cavern, discussing the dearth of open-air cafe dining options 'round these parts.
No, the real architect of this slow zombie takeover is none other than Stardew Valley's resident Zombie King.
Just look at that face.
It's dead. More than dead,
undead. Even the zombies move more than him, because they're just overeager freshman recruits that have yet to learn The Way of True Motionlessness. What, and those mummies? Interns. They haven't even passed the entrance exam yet, and sadly some never learn, smh. The way to pass is not to take it in the first place, as that shows too much effort. Once they eat enough brainze, they eventually gain true understanding of the lazy progress along the way of the undead to achieve a true restful existence.
Zombie invasions are for zombie noobs. There's aways someone who ends up at the bottom of the class.