It is possible to visualize a tool ONLY when an object is located?

Yes – this can be done in tool eventhandlers. Modify the endExecute event.

def endExecute(self):
  # use self.name to get this tool instance
  # Return 1 for OK, 0 for error
  t=GetTool(self.name)
  t.visible =
    (t.getIntValue('Count') >= GetIntValue('Setup.PelletsLimit'))
  return 1

The tool visible property is True if the Count is high.