Hmm, I'm really not sure about this. I thought CFAs had to have a 24/7 number that referees who had been assaulted could call for help, and whilst a referee abuse hotline is a bit more broad ranging it does strike me that there is more than a little bit of a cross over.
The main concern I have here is if a referee calls Ref Support UK having been assaulted and they go to the press with it. And let's face it, they milked the press for all it was worth with the Ryan Hampson story. That then creates all sorts of issues around sub judice, and is likely to cause problems with disciplinary hearings against the player(s) accused of the assault, and potentially even more problems if there is any kind of criminal prosecution planned.
My recommendation would always be to use your CFA in the first instance.