There are many races in the Star Trek universe that are so near-human there may be no discernible difference. The Betazed, and the Trill (unjoined at least), and the Bajorans are all indistinguishable from human on their exterior, just to name a few.
It's also very likely that humans, with their appetite for colonization, would have spread to nearby systems that didn't have an intelligent race living on them. This is borne out time and again in space sci-fi; whether humans have supralight travel or not, they've usually colonized Venus, Mars, Io and other gas giant moons, and built orbital stations around gas giants and "deep space" stations in areas without a solar system but with strategic significance. If they can live there, they can live anywhere.