Expected behavior: Villagers find doors (with the proper sky-access), form a village, and breed when there are enough doors. Bedrock-blocks are ignored in sky-access tests.
Current behavior: Villagers don't breed in the nether, even though they do in Java (because bedrock counts as sky access (e.g. beacons)).
How/what I found in Win10 Bedrock:
1) I tried to get villagers to breed in the nether by removing all of the blocks besides the top layer of bedrock-blocks and then building some houses, but the villagers did not reproduce.
2) Because beacons also require sky-access, I tested activating beacons in front of the doors to see if they had sky access-- they did.
3) I removed the top layer giving the villagers direct access to the sky, they still did not reproduce.
I asked someone to perform this test in java, they got the villagers to breed in the nether at the first step- without needing to remove the bedrock-block roof. Demonstrating that, in Java, villagers can breed in the nether; because they ignore the bedrock-blocks the same way that beacons in both Java and Bedrock versions do.
MCPE-26487 found that Villages do not function as expected in the End. It appears that village mechanics are currently disabled for all dimensions other than the Overworld.