If a commercial product is available from a company to a large audience with support, we should take questions on it.
If there are release candidates, release previews, or anything else that a normal company couldn't get support on, then we shouldn't take those questions.
Getting into the terminology is a bit tricky since RTM means different things to different companies. What we should look at is the availability of supported code.
If a free product is available to a large audience, but there is no direct support from a commercial entity available (many *nix pieces of code), then a couple of things should be factored in.
Is this code meant to be a production release. For example, has it been committed to its repository's stable branch or equivalent?
If there is no "stable" branch equivalent, was a particular release intended for production use? Plenty of prerelease code has a disclaimer like this in the manpage or readme.
Have the maintainers made any "official" statement about whether the code is a stable production release for a specific platform?