Two different things are mixed together here. Point one, in Europe as elsewhere, a person having a personally owned firm pretty much employs whom he wishes. A JW owns a firm, knows of another JW, asks him to start working in his firm, there is nothing illegal to that in Europe.
What IS illegal, is for a business that puts an advertisement asking for work force, to state that only such and such a group of persons will be considered. It is not legal to ask for only men to apply, or women, or JWs, or atheists, or married, or whatever. The thing referred to in the mentioned article, probably is the Polish firm which did such a thing a couple of years ago. How the labour legislation in the Eastern European countries are, I do not know, but in the vast majority of European countries, it would not be allowed. But please note, that the article no way says such a thing is an approvable thing to do, it just states what a company did. As far as I recall, the Polish company had to abandon the atempt, because labour organisations protested, but I am not 100 % sure about that. Anyway, to sum it up, adverts as that are illegal in almost all countries here, but the article just what told what a company had done because of positive experiences with JWs in the work force.