Does Methadone block any affects from Vicodin or Percocet?

Someone told me that since I am on Methadone for chronic back pain, that it blocks any affects that I would get as far as pain relief from Vicodin or Percocet, is this true? So, if I take Methadone there is no sense in my Doctor giving me Vicodin or Percocet for breakthrough pain, is that true?