I suppose in theory as long as the traction pull is less that something that would break a fusion then it would be fine. In general you are looking to unweight the neck rather than stretch it. Perhaps look on the web for research on those forces. Pneumex do a lot of unweighted cervical traction in sitting so there might be some info on their website.

Perhaps test their resilience to it by doing manual traction in supine first and or an over the door type traction setup. All that said is traction the treatment of choice for their signs and symptoms?