It works. When they had the valentines challenge awhile ago, I had an eight sim household doing a reality style competition to see who could get the serial romance aspiration completed first and best - basically it was excuse to have a bunch of sims woohoo but two of the femal contestants fell in love during this, so afterwards I got them married but since they both completed it and wanted children but the custom gender options were not a thing yet I had them both get into a boyfriend relationship with Johnny Zest and used him to knock them both up. They had a total of 6 kids, 3 from each mom and Johnny Zest was the father of all of them - they often invite him over to see the kids and flirt with him in front of each other - one even wandered in during one of the baby making visits, it was all good, and after she kissed her wife.