I don't think I've ever dreamt I was male. I've even dreamt of being pregnant, and of having penis-in-vagina sex as the woman (which is the exact opposite of what I want from sex).
It's pretty distressing, and definitely makes me doubt the validity of my dysphoria. What's worse is that my mother always dreams of herself as a man, which reflects how she's always seen herself, and she likes to use that as proof I'm not really a boy, because even she dreams of herself as a man and she doesn't want to transition or use male pronouns, therefore I certainly shouldn't.
A similar thing is the gender of characters I create in role-playing games. The vast majority of the time, I choose female. According to my mother, if I was truly male, my instinct would be to only make male characters. Which is, of course, what she does. I'm pretty sure it's nonsense, since there are other factors that influence my choice of character, and it's extremely common for men to create mainly female characters... but it still makes me doubt.