In the latest snapshot, I was planning on making a mob that's name is always visible using the CustomNameVisible tag. But when summoning a mob, the name would only appear when looking at it. I tried this tag on other entities, like Armor Stands and dropped Items, and the custom name did appear.

When I did the command: /summon ArmorStand ~ ~ ~

{CustomName:"Bob",CustomNameVisible:true}

the armor stand would have the name "Bob" above it. Even when not looking at the armor stand the name shows like I assume it should.

When doing this command: /summon Villager ~ ~ ~

{CustomName:"Bob",CustomNameVisible:true}

the Villager will display the name, but only when looking at him.

If doing: /summon Villager ~ ~ ~

{CustomName:"Bob",CustomNameVisible:false}

the Villager will have the same results. Will still display the name if looking at the mob.

I've tested this with multiple mobs and non-mob entities.

Just to prove my point, I have a picture of me looking at neither entity, and the Villager's name isn't displaying, but the Armor Stand's name is.
The other picture is of me looking AT the Villager. As you can see my cursor is displaying the Villager's name and since the tag was affecting the Armor Stand, the Armor Stand was also displaying it's name.