recently i watched the episode The hero in the hold and not sure if Teddy was really a ghost or was he really booths hallucination which was caused by the brain tumor. In the scene where brennan and booth are at the cemertary she sees him.

Well in my opinion i think that Teddy was really a ghost but also he could have been booth's hallucination which was said that happened. Like i said before in the question how brennan could have had seen teddy at the cemertary sugguests that he was a ghost but at the same time booth could have easily just hallucinated him. So this could just been something that the HH and Co. were trying to do and make us wonder and think about lol.