For the flat earthers who started researching flat earth as a result of what they've read in the bible for instance, I think for them, yes, flat earth is a dogma. For them, it's contained within the scriptures, and if they believe god is the authority for the bible, then God is the authority for the flat earth. Usually this is bible literalists who interpret every word in the bible in the literal sense. For others, who get sucked in via youtube videos, it isn't dogma, and most of them are questioning the ideas presented.