- Yes, we are supposed to support our videos with text, in as much that the text alone answers the question.
- No, we are not supposed to simply place videos into answers without explanations.
From How do I write a good answer?:
Links to external resources are encouraged, but please add context
around the link so your fellow users will have some idea what it is
and why it’s there. Always quote the most relevant part of an
important link, in case the target site is unreachable or goes
Unfortunately, being able to embed videos, makes people consider them "part" of SE.
Nevertheless, just like with link-only answers, video-only "answers" should be converted to comments below the question (so that they are not answers any more):
If the author does not improve the answer and if no other user goes
ahead and edits the post, it should be converted to a comment. It
still might contain valuable information, but a link alone is not an
answer by SE standards.