That's not quite correct. An out of court statement offered to prove the truth of the matter asserted therein is always hearsay. The exceptions given in that Wikipedia article are not exceptions to it being hearsay. They are exceptions to the rule that hearsay is not admissible.

> The defendant in a criminal case is always available, so any statement they make out of court is never hearsay.

That's also not quite correct. A declarant is considered to be unavailable for example if they refuse to testify about the subject matter despite the court ordering them to. They are also considered to be unavailable if they testify that they cannot remember the subject matter. See rule 804(a) of the Federal Rules of Evidence for the criteria for being unavailable.

(I'm using FRE because that seems to be what others are using. Really though we should be using Missouri's rules of evidence. I think most state's rules of evidence are fairly close to the FRE so that's probably reasonable).