They would. However, as the other person pointed out, it’s faster to just find another compatible race.

Nolan just being a dilf, could have had hundreds if not tens of thousands of kids in the short span of time he was on Earth had he chosen to.

And that’s if he was just taking his time.

Whereas a female Viltrumite can only have about 1 per year, all while waiting for the new female Viltrumites to come of age as well. That’s a very long time to get their numbers up sufficiently.

Theoretically, though, they should have been doing that in the first place, at least as a temporary measure, until they found a compatible species.