I'm guessing that your media from either camera will probably run at a very consistant speed. I would think that your major difficulty would be that they might not run at the same speed as each other though (but they should still be pretty close). I'm not familiar with that Sony model, but if it has digital output capability, use that to transfer through firewire. You will capture both audio and video, but you can ignore the video stream. If you need to reclaim space, you can open the capture in Vegas and render it to a .wav file, then delete the capture.

I'm also going to assume that you didn't stop either camera for the duration or at least for a whole act anyway, and if you did pause between acts, you'll have to do the following operation on each act separately.

Once you have both the video and audio tracks loaded into vegas, find some definitive starting spot that you can use to line the tracks up, preferably before the play starts. Trim the audio to start at that point even if it is after the play starts. Move to the end of the play and see how close your sync is there. If it's off, you can use the Ctrl-drag method on the end of the audio clip to stretch or shrink it to make it the same speed as the video track. If you picked a beginning sync point that was after the start of the play, go back to the beginning and un-trim the audio track back to the beginning of the play. If you get the beginning and end lined up, there shouldn't be any major deviation in sync anywhere in the event.