Stefan, if you are referring to a hump in the middle of the B-pillar (center), then its possible that its a Stroppe-era cage...many of their designs incorporated this detail. That might make it more "valuable" to someone who cares.
To the original poster's Q...NO, removing the top and the roll bar will not negatively affect your tub...unless your tub is totally dilapidated. Otherwise it is supported by 8 body mounts and should be very happy to have the weight off its shoulders. With that said, depending on how old your body mounts are, it may be a good time to put on a new body mount kit (or the WH 1" body lift/body mount combo which is only ~$100). Have FUN!