Folktales are stories passed down through generations, mainly by telling. Some of these stories are genuine and some are made up stories. But some legends of lesser known temples can be found in these Folk tales. So, are Folk Tales acceptable sources?
Folktale are acceptable as an answer till you mention it that way and provide essential source for it too. Source can be a temple inscription, book etc.
But if question explicitly asking for scripture, then its not acceptable. It can be acceptable in the case where you can proof that its not present in any scripture and you are presenting an answer with a folktale with mentioning that its not part of any scripture.