Come on guys - that statement only means "you cannot claim a right to re enter Canada" (as opposed to any Permanent resident or citizen). It always existed on any one's study or work permit irrespective of nature of their stay. As long as you have a valid VISA stamped on passport (the work or study permit is NOT a visa) and all other things you have are in order, you shouldn't have any problem.
CIC's FAQ on moratorium clearly states it does NOT affect existing work permit holders or even those who haven't landed but whose permits were approved.
Though there is always a slight chance that one could be refused entry (some criminal issue, some other suspicion), but i really don't see any grounds in writing to prevent it in the way stated above. You can bring all docs along to be extra cautious and just ask the CBSA to double check their info if they show reluctance.
All those who are suggesting re-entry might be denied, may i please ask for a source / grounds of info, specially since CIC wrote on website clearly that existing ones are unaffected.
Individual cases of some one being returned won't be of much value unless we know for sure that they were REFUSED FOR THIS REASON. They might be short on valid documents. Just my thoughts.