Was the rape scene necessary in Fountainhead? I am an extreme anti-feminist but I still feel it was unnecessary. Did Ayn Rand add that scene to trigger the feminists and make them understand the complexity of consent and sex? (that consent can be given non-verbally for sex)

it wasn't a rape scene. rape is a violent crime. they flirted and then eventually banged. they like rough sex and roleplay.
Rand understates/underestimates the amount of verbal communication that it takes for people to understand each other well. in general, not just in this part of the book. she doesn't present a lot of minor misunderstandings getting cleared up. admittedly i think it's typical to omit those in fiction because they'd just be minor distractions (kinda like scenes where people go to the bathroom -- that's realistic but why put it in?), so that makes it harder to tell what she really thinks. but it's not purely a matter of omission, she also has comments about people judging/understanding others by their appearance and does some things to present some stuff as actually being low communication including the Roark/Dominique early phase relationship.
necessary is a strong word. i don't think it was *necessary*. i don't think the scene is a big deal which is enough to make it unnecessary.
I think Rand put the scene in because sex is part of life and she was sharing ideas about it rather than dodging the issue. I consider her comments about sex to be mixed -- I agree with some points (e.g. pro-happiness attitude), but Rand is more inclined towards traditional gender role kinda stuff than I agree with. she also made a comment against female Presidents. https://www.google.com/search?client=safari&rls=en&q=ayn+rand+female+president