Some of the responses in the Mordenkainen's thread got me wondering how important official material is to the average ENWorld user. So, simple poll.
Second parties are the people using the first-party product directly. In other words...the DM and/or players. So formally, second-party products would be anything custom made by either you as DM or made by your players.1st party + 3rd party + homebrew
So basically "everything except 2nd party" which im fact I have no idea what it is...
The usual issue with Wiki stuff is that careless players find it on the Internet and assume it's official rules, rather than something anyone may have written. This definitely gives me as GM a prejudice against it, I get tired of having to google the source of some unlikely stuff. It's too much like my day job teaching!Never Acceptable: Explicitly-banned things, D&D Wiki content
I've literally never seen a DM who was willing to permit D&D Wiki content, so it gets special mention. Even DMs who are radically permissive, we're talking "let's mix all of 3.5e AND PF, all Dragon Mag content is allowed, AND you can gestalt multi-track PrCs together" level of permissiveness, won't let people use D&D Wiki content. It has that bad of a reputation.