I've been doing a nether survival world for the past few days, and finally managed to get a couple Hoglins into a fenced in area. I bred them together a couple times, then killed off the parents for food, leaving the babies to grow up. At this point they were still acting hostile, and were accepting the crimson fungus.

Now the two Hoglins have grown up, but the game won't let me breed them, nor are they hostile to me anymore. I'm not sure what caused this to happen.

They appear to attempt to breed (facing directly into one another) but no baby is made. They are also still afraid of warped fungus.

Demonstration Video