Hey!
Not usre to get well your workflow but:
"Expose" is a way to manipulate the value from another place in the tree. It's normal if the value of the exposed propertie do not change if you cahange the value of its target
Exposing keyframe values works fine on my side (Smode 9.2.9)
You can also create a link from the value of the keyframe and target your OSC sender to this link