The game considers the womb (a mostly-hidden attribute of the vagina) to be the primary requirement to start a pregnancy, so in this regard female and futa are equivalent. There have been cases in the past where sex changes resulted in a person with a vagina but not a womb, which can be fixed in the laboratory.
If you are playing without mods and neither of the participants are on contraceptives, then pregnancy is simply a matter of ejaculating into the vagina enough times. The wiki entry for the Infertile trait explains:
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If you are playing with AricsExpansion and neither of the participants are on contraceptives, then pregnancy requires you to attempt the impregnation during the fertile part of their cycle, which can be checked in the statistics panel by employing a nurse. Due to a large number of complicated factors and bugs, pregnancy can be tedious to achieve for reasons that can be unclear without reading deep into the save file and scripts.