If you want to give scores to a custom spawned entity you now have to create a fake player and copy the score from the entity over to the player. However this is a bit overengineerd.

Would it be possible to show the entities custom name instead of its UUID? It makes sense for players to let the scoreboard use the custom name rather than an unreadable uuid

The problem is similar to: https://bugs.mojang.com/browse/MC-59052
But as @Skylinerw said "Currently the team prefix/suffix appears to still use the section symbol, so that would still need to be watched out for if it becomes limited a single color only."

Seeing team prefix/suffix are now limited to a single color this becomes an issue again