Thanks ! :)
It's not only in dreams, no, it's just later in the game.
There's also some gameplay logic attached to it, so the game doesn't just assume you impregnated all of them.
That being said, you won't see their belly grow over time or anything, getting a maid pregnant will simply add 2 "look into the future" type scenes (one sfw and one naughty) to the "Carnal Crystal", which will be introduced later in the game.
So it's a little more than just an epilogue, but not fundamentally so, otherwise it simply would've become too much work.