The ovipositor flag on penis does nothing on it's own. However: If you have the "nyrean eggs" perk (from nyrean rockcandy) AND a penis with the ovipositor flag, then you will produce nyrea egg, and expell them during orgasm. But I'm 99% sure that there are no NPC pregnancies from those eggs. It's only for flavour. No idea how it interacts with tail genitals.
The oviposition perk does not affect pregnancies. Pregnancies develop as normal. If you go a certain amount of time WITHOUT getting pregnant, then you will get pregnant with eggs and lay them.
I suggest checking out the egg trainer. It's sold by Lerris on Tavros station for about 10k. It unlocks alot of egg centric content. You can take all of the following options either vaginally, analy or both at the same time.
What it can do:
1. Impregnates you with eggs and you lay them the same scene.
2. Impregnates you with eggs that you carry for about 7 days, then lay them
4. Faux pregnancy: You will be forever pergnant with one egg. You will never lay it. You can remove it with the egg trainer.
5. Ovalasting Egg: Injects a special egg into you. When you take cum vaginally (or analy, depending where the eggtrainer put the egg) you will get pregnant with eggs and lay them after a certain amount of time. This will take priority over any other pregnancy, until you remove this special egg with the egg trainer. Then pregnancys work as usual again.
At first, you can only use option 1. The more you use the egg trainer, the more options you unlock. I think doing option 1. five times unlocks all the content.