To use an SWU outside of region one, you must have at least a W fare basis. You won't be able to use the upgrade on Virgin Blue, but can use it on the UA metal segments. It is hard to say what the chances are. Just because there are some C seats left does not mean they will clear. There may be several people ahead of you on the waitlist, and UA is trying to sell the reamining C seats. Looking on ual.com for "I" or "NC" inventory with an award dummy booking will reveal the chances. Also, you can call and see if there is any confirmable upgrade space.