My mother, myself and my sister are somewhat adventurous with our food choices. My father, on the other hand, is a typical meat and potatoes kind of guy. I have eaten at about 90% of restaurants on WDW property (both parks and resorts). That being said, I would feel comfortable taking my father to most of the WDW restaurants, with a few exceptions.
Being a vegetarian myself, I am quite accustomed to asking for a meal without certain ingredients or making substitutions, and Disney is very accommodating. I would imagine they would be the same way for the "American meat and potatoes" eaters out there. Even Jiko, with its African menu, has a fillet with red wine reduction on top of macaroni and cheese. Certainly, it could be ordered without the red wine reduction, thereby making it more plain. I would not, however, take my father to Boma (even though he would find something to eat, there wouldn't be much) or somewhere like Teppan Edo as he does not like Japanese food.
So don't worry too much about finding food you will eat.