I too am I interested if there is a proper way to do this. We did do this but didn’t test the rigging (because it was a cowl for the head).
Our steps were (ill use your uniform as an example). Rig the Uniform to certain bones of the character and weight them so they deform like the character itself. Export just the Uniform with the bones etc…
Then when you import them into UE4. Import them as Skeletal mesh but instead of letting it create the skeleton select your Characters skeleton. This will work because the bone names etc… are the same.
Then attach the uniform to your character via a socket. Then play an animation. Unfortunately we didn’t have an animation for the head so couldn’t tell if it deformed with it. But it should do because the animation drives the characters skeleton and the Uniform is using that skeleton. The only problem we have with this way is when you get round to Apex cloth the cloth passes through the character because you can’t set up collision in Apex tool due to it only being the uniform not the whole character.
If you want easy Blueprint code to attach the uniform to him via socket, first set up the socket. You can put the Uniform skeletal mesh into a Blueprint (parent Actor) this gives you more options to add stuff to just the Uniform not character etc… Then in your Character BP on Event Begin Play. ‘Spawn actor from class’, select UniformBP then plug the actor from spawn actor node to ‘Attach to’ and get Mesh and plug that into ‘attach to’ Parent node and specify the socket name. This means on Beginplay it will attach the Uniform to the mesh.
Let me know how it goes.