Inversions like we are used to play on a keyboard don't mean much to a guitar player: they think of "frets" instead. So, better tell him to play just a D7 or a C or and then leave to his musical taste to find the proper position on the guitar neck.
As a general rule, the chords played on a guitar shouldn't overlap (in terms of frequencies) with the chords played on the keyboard, to avoid the so called "sonic mud".
The same rule applies for the bass player and whatever is played with the left hand on the keyboard.