D&D is a parody of normal morality (even logically due to the present and watchful gods). Don't expect any grey from their "evil" races.
I don't agree.
(A)D&D morality can be as broad or narrow, as flexible or as immutable, as any given DM/group deems it to be.
There is plenty of room for shades of gray, and never has an "evil" alignment implied, in and of itself, an absence of good, or vice versa.
You don't see conquering armies raping men or boys openly no matter how "evil" (for instance, lets use the khmer rouge in Cambodia, after the US bombardments, just as a example) they are, do you?
Such things are not totaly unheard of. Less common than the systematic rape of women, for a variety of reasons, but not unheard of. Biggest reason it's not a matter of policy is because males cannot give birth, so the lasting effects on the enemy society are usually small, which in turn limits it's appeal as a strategy.
As for the alignment of rape, most would consider it an evil act, but it's not limited to evil beings and not all evil beings are going to be tolerant of it.
The whole concept of alignment grates me something huge, specifically because it's quantifying and reifying something that should not be in the name of mechanics and their "lore" and i use the word loosely.
It's why you get people asking for portraits that "look evil" or "look good". Did Cheney "look evil" to you?
I'm not sure your concept of alignment matches the intended use of it, or how it's used in practice.
People do tend to misinterpret the place alignment has, or even confuse it with entirely different aspects of a character. Alignment is not personality or style, and has no outward appearance.