Anything with a MIDI output can be used as a MIDI controller. It doesn't matter what it is; a 1 in/1 out MIDI USB cable only costs $30 or so. No computer recognizes what kind of MIDI device is on the other end - what they recognize is that MIDI USB interface. (this is why Logic will never know whether it's a new Motif XF or an ancient JX3P on the other end; all it talks to is the interface).
What real piano are you talking about? I don't know if Yamaha's SilentPiano has a MIDI out. It would be a sensible thing to do, given the fact that there's already a scanning mechanism in place to control the internal sound module - but sensible is not always in their dictionary
(also, the specs stay pretty quiet on this)