The three Dreamcatchers' common sense and virtues were slowly corrupted the longer they were exposed to Vaan's daily activities. However, since they were so chaste and innocent, they did not even know how to relieve themselves.
As such, they helplessly allowed the carnal heat to accumulate in their bodies until they fainted with nosebleeds.
Hecate should have known about the depraved side of Pangean Humans, especially in the witch kingdoms. As such, she should have also known what she was sending her Dreamcatchers into by making them follow Vaan.
She might not have made the same choice if he didn't have the Boundless Sea and Sky Aura.
However, since she did, she practically gave Vaan the green card to fool around with her Dreamcatchers, especially when she told him not to bully them too much.
That said, the Dreamcatchers were still Late-stage Rank 6 Divine Beings.
