I dislike Sidewinder and Oracle. I mean, there were cooler ones, I liked Syd as Freelancer. Not so much as Phoenix. And Vaughn as boyscout *smirk* I just wish that there was something different for them. Honestly, I doubt they have much meaning to the charater.
I think Oracle definately has a meaning. In fact, an oracle is a shrine consecrated to the worship and consultation of a prophetic deity. I think we're being told that Rachel has a big role in Prophet 5.
My all-time fave Syd callsign is Freelancer, but each one she's had has been for a reason. Freelancer was her CIA callsign when she was a double-agent. Phoenix is her call-sign because she came back from the dead, risen from the ashes... like the mythical Phoenix bird... which I think fits. Might have worked better back in Season 3 though. *lol*