Let's look at the edition prior...
Middenheim: City of the White Wolf (1e) gives the basic overview of the legal system of the Empire. It doesn't specifically call out sexual offenses, but does call out blasphemy and heresy.
We know that the Slaneeshi cult is both proscribed and embraces lechery, debauchery, bondage, fetishism, and pansexuality (sex acts with anything).
The insanities do not include Homosexuality nor homophobia, but do include gynophobia and androphobia, but not one's own gender. Likewise, hatred of the opposite gender is an insanity.
The only homosexual characters I recall are all chaos worshipers.
We know that, of the 5 PC races in 1E, all 4 core (Human, Elf, Dwarf, Halfling) have males and females, marriage, and similar family sizes. It is noted in Tome of Corruption that mutant children of the non-Human are quickly destroyed.
How? Because of the 1E character pack. It gives expanded character background, specifies the genders, and does not provide for "adopted into non-heteronormative family."
All the family specified is 1 man, 1 woman, and their children, with the potential that one or both parents are no longer alive.
And On To Second Ed...
Laws and Trials
The legal system is explained in Sigmar's Heirs, with advanced trial rules in the WFRP Companion.
The corebook still specifies all 4 core races have both male and female members, there are gender differences in naming (page 27, example names on the tables).
We also see in the description of Slaneesh that Slaneesh is, itself, hermaphroditic and bisexual, with implications of pansexual and sado-masochistic tendencies. Like 1E, however, homosexuality isn't in the insanities.
We do not have the family generation in 2E - thus we can say less about what is normal.
The society within the setting is a caricature of the late medieval and early renaissance period. A period of high superstition, and many religious persecutions and intolerances. Conformity is imposed, enforced often by the extremes of execution and maiming.
A Note on the Meaning of Sexual & Gender
Sexual, as a technical term, has a scientific meaning of reproducing by mixing genetic material from two parents, to create the offspring.
Gender has, in stable terms, essentially 4 basic gender types: Male, Female, Hermaphrodite, other intersex, and Neuter.
Females generate the egg cell, and either deliver the egg or the resultant child. In mammalian forms, this is always after fertilization by sperm.
Males generate the sperm cells, and deliver them to the egg, either before or after it's delivered. In mammalian forms, this is always before delivery.
Hermaphrodites have both male and female reproductive systems. In most cases, arranged such that an individual is not capable of self-impregnating. No mamalian species is normally hermaphroditic, while some molluscs and worms are.
Neuter individuals lack either gender... and in mammalian forms, are sterile.
All the races shown are shown to have two biological genders: male and female. Thus, all the races are implied strongly to have male-female sexual reproduction.
Certain non-mammalian forms have sequential gender - male at one range of ages, female at other age ranges.
A few species have only one gender as normative, female, and reproduce asexually, but those are fish or lizards.
This leads to answering the sub-question of Dwarven sexuality as "male-female intercourse appears to be the norm."
Given the association with Slaneesh, a herm child would likely be culled in Elf or Dwarf society, and quite possibly mutilated into an apparent female in Human and/or Halfling society, if allowed to live. Hermaphrodites are not included on the mutations tables, nor on the gender tables, nor in the 1E family tables, so none of the races covered have a significant rate of hermaphroditism.
Reality, however, is far messier with gender in mammals - the tiny fraction of individuals who are neither fully male nor fully female biologically are a spectrum, with a rare few fully functional herms, and a variety of non-reproductive herms, ambiguous genitalia, and such. Intersex, including true herms, are about 1:1500 to 1:2000 in the general population. cite
Gender and the Game
We can assume that this hold to its relatively standard rates of about 1 per 1500 or fewer individuals expressing intersex, and isn't included on the tables simply due to granularity.
Or, we can assume that intersex individuals would be culled, and the parents probably neutered and/or burned at the stake by a paranoid and fearful population. The charge would be Worship of Slaneesh, and the deformation of the intersex child would be more than plenty proof for most witch hunters.
We have no reason to assume any of the core races to be outside the two gender paradigm (with potential under 1% deviation), normal male-female procreative copulation and all individuals having one biologic male parent and one biologic female parent, and having been gestated within.
We do know, however, that not all intelligent races in the Warhammer world follow this. The corebook races, however, are pretty much demi-humans, and not really outside human norms.
Sexuality amongst the corebook races is apparently pretty heteronormative.
The game avoids labeling homosexuality neither as proscribed, criminal, nor insanity, nor as an aspect of Slaneesh. It does subtlety imply this, however.
The intolerant society would most likely be rabidly heteronormative, as was historical early renaissance Germany - which the Empire is a parody of.