According to Chuggaaconroy there was a boss ghost that was meant to be in the safari room but he got removed for being too scary. He claimed he heard it in Nintendo Power but I can find nothing about it when Googling it.
I do believe I read something about a removed ghost in the safari room on a mario website, but I think that the Nintendo power info is just a joke, becasue I think I remember reading it in their "Pulse" section (which, can often yeild fake info for the sake of comedy) E.G. Reader: I heard that there was a removed portrait ghost in the safari room, is this true? NP: Yes, but this Australian hunter wants your head on his wall so much, it was too scary to be put in! I may not have made the best joke, but you should get what I mean.