You are correct that they would be taken by the world, and that it would be possible to recreate similar ones using the magic of Geardagas given time and practice. In regards to the second ability, as it's Divination in a sense (seeking information), he would need to focus more down that route and look into those who do something similar; the Wilde oft brings back those who are terrorized by nightmares, and there are Witches who specialize in soothing those mental worries and blocks just the same.

So, while it isn't taboo, it does require something of a specialized training and "permit" in a sense by the Coven to know you're a practitioner of the art.