Customer has some metal trays (moist area) & needed to add heat for they're application. They were supplied silicone heaters that attach to the trays & they say they're getting shocked. The silicone heaters don't have a ground and the customer is reading 60V to ground. Could they just run a ground to the trays to alleviate the problem?

First - A qualified electrician needs to evaluate this "on site"...
This is a building with people who are being exposed to a serious risk
so guessing at the answer is not an option. You will be liable if you put your hands on this issue.

That being said, this could be one of the heaters with insulation that has failed
or this could be something unrelated to the heaters but by some coincidence is energizing the conveyor.

If you turn the power off to the heaters and the 60 volts goes away obviously you have narrowed down the problem to the heaters.

Since you are now dealing with protecting the public welfare you need to certain of the cause and the safety of the repair.
Be Careful

Depending on Amperage, 60VAc to ground can be dangerous. Why fool around. Grounding them only puts 60 VAC on to the ground. Turn them off until the problem is solved.