I AFK a lot.
My primary AFK location has a nether portal close by (roughly 20 meters).
Zombie pigmen spawn occasionally in it, then disappear back to the nether.
This morning, I went into the nether, and was greeted by about 50 zombie pigmen. All probably in the same chunk as the portal.
Are these pigmen counting against the mob cap in the overworld?
Best Answer
In singleplayer, the nether is not loaded by default, so any pigmen (or other mobs) that spawn in the overworld and wander through the portal don't move or count towards the mob count anymore, until you enter the nether. This is one way to get around the cap for naturally spawned mobs, storing the mobs in the nether until it is time to kill them.
This can lead to dangerous (for your computer/framerate) amounts of mobs in the area around the portal once you do enter the nether though, so if it is not part of your design, turn off your portal before afking. Doing so will also keep the pigmen from spawning in the overworld.