A 200K player model animated in UE4 sure why not but is rather excessive. Animating 200k in say something like Maya or Max is not recommended and although can do the job they are more generalized tools. MotionBuilder on the other hand can handle 200K no problem.
As for optimization UE4 is what’s called a closed edit environment that supplies features as part of the design towards the final output.
Not sure as to reason to reduce a in production model in the original post but in most cases you would want to increase or decrease the asset resolution inside of UE4 using tessellation and Simplygon LOD’s.