You didn't ask me, but I'm gonna chime in anyway, eflie. Unless you wrap them really really well, I think the onion is gonna thaw out rather wierdly (onions are full of water that crystallizes when frozen, etc.). I have the same fear for the butter, but someone with more knowledge than me should jump in with more science and details.
If the rolls are already "made", I think the closer to room temp they get before serving the better they will taste. Afraid the rolls may get soggy with all that stuff on them, tho.
Kool Aid - Think before you drink.