When I do this command 

/summon minecraft:iron_golem ~ ~ ~ {Attributes:[{Name:generic.followRange,Base:100}]}

The line of sight of the iron golem is not affected at all. Even if I set it to only 5 (which should mean it cannot see anything further away than 4 blocks), it retains its default line of sight. It's the same case for Wither Skeletons, and presumably some other mobs but I haven't tested them.