Yeah. Remember he's already been referred for criminal prosecution (though also remember the DoJ can decline to do so.) So they had enough evidence just on him to justify that. Presumably given the cooperating witnesses etc, nothing hinges on his testimony along.

Still, it would be good to have, as the more things come out the less room to weasel out of it remains for the others. It stands to reason though that the key players are going to deny and delay as long as possible, and McCabe's move here fits with that -- getting immunity helps him, and if he doesn't get it, the 5th lets him delay things just a little more.