I wouldn't be too concerned myself. When you're bringing guests on in a capacity related to games from a media/interview style perspective, your primary application under law is fair use. So, you're fairly well protected in that regard. There is a certain implication involved that if you run a YouTube show, invite someone onto the show, that this show will then be uploaded to YouTube and not just sit idle on a hard drive somewhere. That, along with the fair use defense would make it difficult for someone to justify taking it down.
In a lot of respects, what you've described is different from a collab and would be in essence, no different from a news station conducting an interview.
Generally speaking, what you're referencing with the idea of a waiver is something utilized in art more often than other areas. It's called an Artist Release and is something generally designed around using artists work in your own production. Often it will be used for people specifically under the name Model Release, where a person is present in an artistic production. I don't see these applications really being relevant to what you're talking about doing.
