Don't emotes just create empties above the player with emitters attached to them?
Pretty sure the emote spawns an explosion or a projectile.
There is no way to directly attach an emitter to a player (I assume you want the emitter to move around with the player too). You can, however, attach an image to a player and have an emitter on that. Then it will move around with the player. Many add-ons already do this.
The problem, however, is that you can have only 4 images on a player at the same time. That means, if another add-on also wants to add an image to put an emitter (or a default function) then your emitter is gone.
Another way I can think of would be to create a new AIPlayer (maybe even create a custom playertype with an empty model and just one mount node), make it invisible, mount it to the player at the node where you want it at and then attach the image to that. As long as nothing is controlling the AIPlayer, it will have the same rotation as the node it is mounted on.
So, it is possible, but it will be a very hacky implementation.