Of course someone without an internal monologue can have intrusive thoughts! Do you think intrusive thoughts have to come in the form of a monologue? You don't have intrusive 'scenes' in your everyday experience?
I think it is fair to say that internal dialog includes whatever mode someone primarily thinks with internally. If it is words, images, or kinesthetic, only the modality is different. I don't see how these modes wouldn't constitute internal dialog if that's how people think internally. These are the primary ways people generally do form their internal world.
There are also olfactory (imagine smelling cinnamon in a slice of apple pie) and gustatory (think of vinegar). These two don't tend to occur in dialog form, but they can enhance or reinforce the other modes. Animals like dogs might not agree with that suggestion.