In regards to a possible "It" connection: "Also, Stan says that "In this universe there might grow roses which sing," (It p411) which alludes to the Rose in the vacant lot."
I doubt that one. In that passage, Stan is talking about how the sight of dead boys walking offended his logical mind. Offenses like "a square moon that rises in the sky", "some triangles that have four sides", and the aforementioned roses that could sing.
Those are all things that might drive you crazy if you saw them, such as Stan's dead boys.