After I updated to Beta 5 my custom ringtones did not show up when I went to change the new message tone. I unchecked to sync ringtones in iTunes, Applied and then re-checked it and applied again. Afterwards they showed up.
I did notice something interesting, a custom tone I was using for ringtones stopped working. Another custom tone I had worked fine. The clip that was not working was about 15 seconds long, the one that worked was 2 seconds. I redid the clip to be 8 seconds long and it works again. I wonder if Apple put a limit on the clip length for text tones in this beta?