Its definitely possible. You have to keep in mind that nobodies alone are rare which means the humanoid ones are even rarer, the rarest really. I'm sure their is others but they'd be highly few in number. Plus due to their human look and lack of threat by Organization they likely could or have integrated into society and living that normal life likely awoke a heart within them.
In the end you'd likely not see any of them for those various reasons. If we saw another humanoid nobody again it'd be due to Xehanort somehow or some new villain with similar goals to him or Marluxia. Since being able to form a heart on their own kinda defeats any reason for them to be antagonistic unless they're just a power hungry type.