My take is this, formed when I was considering such a project and thought I might someday have the time and funds to make it work.

I had similar qualms about the RiffTrax commentary.

For the other two I was going to put an attribution: who made it, and the web site logo.

And I'd probably do the same with RiffTrax with the moral imperative that if used (enjoyed? not sure) then a small donation / user's fee was due the crew at RiffTrax.

The track even indicates the likelihood that the track will propagate widely on the Internet. At least this would be a project that encouraged payment where due. Doesn't make it right, of course...