Actually North Koreans worked in PL well before PiS came to power. The EU talks tough about NK yet they have no problems with NK running hostels and restaurants in Germany.
Many of the NK's who came to Poland, like the Vietnamese, came during the PRL years. Most of the NK's that are in PL are located in the tri cities where they are employed as ship builders and some in agriculture. These are legal activities. There is no ban on hiring North Korean workers and PO never did anything about the NK's working in Gdansk during their term in power either... so your assumption that PiS are actively doing business with DPRK is false as it is mostly private individuals/sp zoo's that are contracting NK's for the cheap labor. This was done before PO's term, during PO's term, and is still occurring under PiS.
Quite frankly, most Poles simply don't care about NK and don't care about the few thousand workers in the country....
Also, I'm pretty sure one of the high up Kims was up until very recently the ambassador to Poland and currently lives in Warsaw in one of the fancy neighborhoods.
The PiS regime are nevertheless happy to do business with DPRK.
This article says otherwise
But according to the foreign ministry in Warsaw, not one work visa was issued to a North Korean national after the tests. In 2015, 156 work visas and 482 work permits were issued.
The Polish government also stated that it is looking into the case of a local shipbuilding company that was employing North Korean workers at its sites.