That is -- I think -- exactly what this feature does.
The MacPro would run the client software for the feature. The MBP would run the server. Clients regularly check to see if the server is available. When the server becomes available the client (MacPro) accepts keyboard / mouse input directly from the server (MBP) once focus is given to the client. Focus is usually handed off either by a keyboard command or by scrolling the mouse off the edge of the screen of the server.
Check out
Barrier.
I believe you can install Barrier through
HomeBrew (via a 'cask' -- and I'm still not totally sure what the difference between a straight brew and a cask is
.. except in real life. i'm very familiar with that difference).