I hope I didn't confuse anybody. As an all-in answer, I did conflate the terms vst/synthesis, sampling, preset, software, and by extension, loops and other "production work materials."
It is not the materials themselves that are "legal" or not, it is there use that is legal or not. In the example above, and in answer to the OP's original question-- yes, he would own the music he writes with any vst/synth/plug-in. But I'd be careful with a blanket statement such as "sampling is legal." That might give people the wrong idea. Sampling what? Sampling something from a record, CD, movie/DVD, or sampling peoples voices live (on the street, or in a live setting such as a concert or play, or from the radio, for instance)? You might think so, but you'd need permission; this ground has been covered 1,000,000,000,000,000 times here on this site, and on many others. Sampling birds, trucks going by, machinery, various instruments and sound sources? Yes (usually).
Most people, accidentally or intentionally misunderstand and misuse the "fair use" clause-- that is for educational purposes (formal education and scholarly inquiry, in a classroom or academic setting), or for newsworthy or news-based broadcast and print media use. Also legitimate satire or parody. But just because you want to use something does not make it "fair use." Nor does it have anything to do with whether or not you are "making any money off of it." Copyright ownership is copyright ownership. It gives and reserves for the bearer exclusive _rights_ to make _copies_ of the creation/idea/actualized concept in-question.
These are thorny questions, very often misunderstood by even those working at various levels in the music industry and other areas of the "culture biz." But again, in response to the OP, yeah, you're ok using vsts for your productions. Just don't try to pass off the software as your own and/or act as an unauthorized re-seller. This is usually the crux of the average user's agreements that accompanies such software.
GJ