No you'll have to do a full re-install as the Beta is just that, a beta and you'll need the full version of the released software to use with the retail key.
One of the good things with home server though is that you can just re-install Vail WHS as the OS and not any of the files, videos, photos that you have put on there.
Though if it was me I would do a full rebuild if I was you once the full version has come out of the whole system O/S and the data, just in case anything has changed. Especially with the new file system set up that Vail is introducing.
Taff