Some people claim that asking for help to other than god is polytheism.
Their going to doctor is a type of seeking a help from a specialist even though they do not say by their tongue that they are getting help from the doctor. Acting shirk is enough. Also they should not ask any question from anyone or request anything from any one because all these are shirk. He can not benefit us unless Allah wishes to. Imam Ali and all the martyrs are alive as Quran clearly testifies, though they are not on the earth.