In the most legal sense it's true that it's not ok, and I see notes about artists being alive or not. Copyrights expire after death, but that takes at least 50 and can even be up to 90 years after the original creator's death depending on your country.
Although I do agree with Saga that it's unlikely anybody would care, I am (being a game designer myself), mostly not for it to take any music unless the artist either explicitly granted me permission or if a piece of music, regardless of the site on which I obtained it, or has a license that explicitly allows it like most CC licenses (check the license,as some CC licenses can still be pretty restrictive). Actually that goes for anything I add to my game, from code to music, to even art if I can't create it myself, well anything. Since even if it's unlikely anybody will care, if you by chance find somebody who does care you can still have a problem.
Having been a moderator of a big gamedev community, I've seen some fights over artwork, music, stolen code, well whatever (even about stuff that had a free license, go figure), and if you can at least make sure your hands are 100% clean, you can at least hold a good story in case trouble comes. Out of professional reasons I won't go into the deep of cases I've come past, but I can tell ya, those fights were really really terrible... We all know the internet can be cruel, but in some cases people really went far.