If you have to make an offset on a .SCC file you can do that in DVD SP. However, there is no way of checking it besides building a disc, burning it and take it to another set (the apple DVD player is not too reliable in this department). Of course this is a very time consuming process.
SccOffset gives you instant results. Just import your assets and set an offset, playback of the captions is instant.
When satisfied you can either have the file converted, or use the found offset to set it in your DVD authoring package.
You can choose from a variety of input formats, even MpegII elementary streams. If you have elementary streams, you can select/assign the audio track to be played sync with the video.