Salt is the regular wicket keeper for the blast. Did it most of last season. You’re right, he does it because there isn’t really anyone else. Brown doesn’t play much 20/20.
Not sure why Brown doesn't play, he's a pretty aggressive batsman. But there is someone else; Oli Carter is in the 14-man squad so he may well play in the future. And Ali Orr had an impressive first class debut, he may well appear in future squads too