I assume you are just exporting through FBX
with genitals when you export, you usually have 2 things. The mesh with the genital, and the shell mesh that covers the genitals. In addition to that, the genitals have two textures. The mesh that is united with the body often shares the body UV texture to match the skin color of the body. The shell will have its own uv with the details for the genital (veins for example, head/gland color). It could be that in unity, it is not blending through the shell very well to see the skin underneath it.
I personally prefer to load the asset in blender, its been a while but I think I make a version of the body mesh that is just the genitals, I uv transfer from the shell to this other mesh I make, and then I reatatch the genital to the main mesh, then it is safe for me to remove the shell mesh. this way the body is one mesh, and it has both textures. I can mix the shaders to get the genital to look just right, and then I bake it as 1 unified texture.
I have thought about making a tutorial on this, but I've been distracted. If anyone has a less cumbersome solution, that would be dope.