Your ethymological research is correct. However, the name of Arius has never become common in Poland and you may find it only in historical dissertations on the theological doctrine of Arius and Arianism. In fact, children have not been given this name because Arius is not a saint, thus not a name that a baptised child could be given in Poland – predominantly a catholic community. Interesting, that Arius is not a saint or blessed within the Arian doctrine either. So Arians have not given this name to their children either, when they still had their communes in Poland.

Therefore, the name "Arius" of genuine Latin origin is in Polish "Ariusz", likewise most historic latin names with "us" ending.
Regards
Marek