As many have stated, it depends on the individual and his/her ability to perform in the 'real' airplane. A sim instructor will most likely be well versed on systems, procedures and such, but if long out of the cockpitmay be unfamiliar with how it really works. I flew with a Flight Safety Citation instructor years ago and had to verbally encourage and subsequently manipulate controls on landing to satisfy my comfort zone.
Recommend Chief Pilot or supervisor fly with the guy/gal and determine if he/she is fit to fly.
Good luck!
Bingo