This question has generated two answers (one deleted) that link to reddit discussions or sources.
Is there a policy on whether or not links to Reddit are legitimate for an answer or is that handled through up/down votes? If there isn't, should there be?
This includes cases where a 'discussion' is referenced as well as compilation of data done by redditor (which may or may not be complete or correct.) This is not a question about linking in general, but linking to something as integral part of an answer.
Whether or not the source is any good, or it makes for a decent citation or reference for the answer, is up to you: resolve this with upvotes/downvotes. Would a D&D guide be any different whether it was published on Giants in the Playground or Reddit?
There's no policy against linking to Reddit (see dopplegreener's answer) nor should there need to be a policy without a clear reason (even something like the dreaded dandwiki isn't forbidden).
The answers you are referring to have likely been downvoted and/or deleted due to being low quality (in my opinion).
One is effectively a copy/paste of the content of a linked Reddit thread without adding any significant transformative commentary. There are scenarios where a discussion could be meaningful content, but not without substantial content in the answer itself.
The other refers to a Reddit thread but doesn't really incorporate its content in any noticeable way. It includes some scattered commentary but doesn't really look to answer the OP's question. For example, it addresses the mechanics of a different class than the one the OP asked about. So the Reddit thread is only part of the problem in that it isn't helpful.
The references to Reddit aren't the problem. It's just a case of two problematic answers coincidentally referring to external sources.