No, you can polarize with both Olwen and Elen, since they marry in the course of their mythic narratives. By "virgin goddesses" I mean goddesses like Minerva, who are permanently virginal. Sul falls into that category; the Romans recognized that when they equated her with Minerva. Ceridwen does not -- in the myths, she's married and has children, and she's also the original of the Loathly Lady in the Arthurian legends, who turns into a beautiful woman and marries Gawain.

The best way to gauge the potential for polarity work with a deity is to get familiar with his or her myths and legends. If they marry, or have less formal relations, they're appropriate for polarity work, and the more central marriage or mating is in their legends, the more appropriate they are. (Thus Olwen and Elen are both well suited to the work, since in both legends the marriage is the central plot engine.)