Our guineas started flying around in the tractor and I think, banged themselves all up, causing deaths. When I was down to 6 guineas, we caught them and put them in the coop with the chickens. They are about to get their own quarters (almost finished addition) and then the plan is for us to garden with them after they know to come back to the coop.
So personally, from my experience, I wouldn't use a tractor again with them, unless very short term and have a back-up plan ready for if it doesn't work out.