Dwarves only have children with their spouses. I don't know why you'd think it would be any other way.
The wiki is back up now. Its actually NOT stated anywhere in the wiki anywhere one way or the other. So I'll have to take your and Innominate's words for this.
Also, I was under the impression that dwarves mated via spores as well. Are all husbands their baby's daddy? Is this new or has it always been this way? I'm not talking about infidelity (an interesting subject in itself!) but rather about rogue dwarf spores floating around inpregnating other people's wives! Do unmarried dwarf women get impregnated, or is marriage a prerequisite? I think a couple of those questions can be answered on the wiki, but its down atm.
"Spores" isn't really the most accurate term for how breeding seems to work in DF. It's just a player-base term for how things can breed over long distances.
Essentially, every so often (per season? Toadykerchief - the amalgamation of Toady One and Footkerchief - might know) a female is selected to breed. It chooses from among a list of available males and is instantly, by "spooky action over distance", impregnated. This is the "spore" behaviour. For civilisation creatures, the list of available males is confined to ones to which they are married. For now, this means just one male per female and vice versa.
Though I really wish polygamy and infidelity were entity ethics options, and one day fodder for procedural culture: it would be awesome to have two dwarf civilisations/guilds at odds because one group thought the other were "skanks" and they were in turn thought of as "prudes". It would be especially Fun for the player having to deal with a fortress where dozens of babies were produced each year because birth control doesn't exist and the dwarves had non-stop polygamous sex.
On the other hand, you get a new batch of recruits every time your children mature. A fortress with new babies every year will eventually have a constant supply of goblin fodder.
Yes! Exactly what I meant about infidelity being an interesting topic! Obviously its represents a cultural more, so it has no bearing on this Arc, but its something to think about. ;p
I'm aware that there are no actual "spores" I just find the concept so amusing that I felt the need to perpetrate it. "spooky action at a distance" is a good way to say too lol. So dwarves DO reproduce by spores, their spores are just very good at homing in on their wives. Actually now that I think about its more like the female decides to get pregnant so she thinks about some male REALLY hard and POOF, she's pregnant.
Anyway, the fact that dwarf spores are restricted in some way in who can impregnate who (even if its totally uncontrollable by the player) gives me hope that we'll at some point be able to control the spores of animals and run animal breeding programs that actually accomplish something, eventually.