Well, first of all Roadside Picnic was actually published by the state. Then, the state funded a rather expensive Tarkovsky movie, inspired by the book ("Stalker"). I think I even had this book at parent's apartment. Plenty of Strugatsky's brothers novels were actually published by the state publishing houses. I think they ran into some problems with their more satirical pieces ("Tale of Troika" comes to mind, for example).

Your description of artists' life is pretty simplistic and one-sided. There were some people who did propaganda posters, but there were many things that existed outside the political domain, from book illustrations, to paintings with less ideological overtones, to working in theater. There was also Soviet cinema and animation, which would hardly be seen as only a propaganda vehicle, there was a lot of very nuanced works, which raised important questions. A lot of good stuff was shelved, or circulated underground of course.