Q: Can I win with Citizens of the Candy Kingdom if I have Candy Zombies, if they’re my only Creeper?

A: Yes. Though the Goal does not call out Candy Zombies specifically, they are clearly marked Candy People, and, as long as they’re your ONLY Creeper, that’s enough to count as “unless the Goal says otherwise” (regarding them preventing a win).

Thematically, Princess Bubblegum certainly still cares about them and would consider them citizens of her kingdom, even though they are afflicted with the zombie sickness.