If he has a standard length swingarm this could be dangerous.
The clearance between the tire and the swingarm is not very much.
At high speeds the tire expands outwards (check a top fueler when it does a burnout - WOW).
Barry Sheen had a crash a long time ago that was attributed to the tire expanding at speed and rubbing the swingarm. He had bias ply tires, but at 200 mph that tire wants to expand outwards and wants to hit that swingarm.
My advice is to keep it a distance away that you feel safe, as if it rubs at high speed you will be down (and probably out)
JMO