It's the same situation in the U.K. as well; there would be no immunity.
Just quickly going back to the previous point, again, in relation to the U.K. system, which as I've described is a fairly ad hoc system or witness protection program, in my interviews with police officers who are running the program in Strathclyde the thing they were probably most concerned about was making sure witnesses didn't materially benefit as a result of relocation, because they were very concerned that their evidence would then be seen to have been tainted or bought by the police and prosecution authorities.
In terms of setting people up in new communities and giving them support, it was an absolute rule that they were never given any financial payments to assist them, that there was no giving of cash payments to witnesses, because they were concerned that these could be used by the defence in any criminal trial to suggest that their evidence had been bought.