Well, realistically and statistically speaking, chances that an Alien even has similar reproductive organs to humans are way slimmer than your chances or winning the lottery twice in a row, so I doubt it would be an issue in any case.
Speaking of Kickstarter, you could now ask yourself if you're willing to bang Hitler. And no, that's not hyperbole: https://www.kickstarter.com/projects/devgru-p/mein-waifu-is-the-fuhrer-a-parody-visual-novel?ref=discovery_category_popular
How can I put this.... if the Alien can talk.... poop or hear then I've got 3 ideas of ways to have sex with it... I mean, they're gonna have eyesockets of some type as well?
If you think incompatible reproductive organs would stop someone having sex with something else then you should have a word with the guys who bang their cars or body pillows.
Fancy hearing me on an amateur podcast with friends gushing over one of my favourite games? https://youtu.be/1I7JfMMxhf8