Is is inappropriate to bring a +1 to a gradate school recruiting weekend?
Bringing a significant other who would be relocating with you to a recruiting weekend is acceptable. In fact, some schools/departments would encourage it. We routinely welcomed SO to our recruiting weekend and saw it as a "good sign" when prospects brought such a person.

I would not bring your parents (would make you seem juvenile, and I have never seen this in practice) and I would also hesitate to bring a significant other who would not be relocating with you.

The next question is which events the SO should attend. This is probably a good question for whoever is planning the recruiting weekend. I would expect the SO to attend social and student-only events (meals, tours, social evening), but not academic events.