Sure you can coalesce the RBS tablespace, it is just the same as any other tablespace. The database sistem could not have any idea that a particular tablespace is ment only for rollbacks (as opposed to TEMP tablespace, if you create it as "TEMPORARY"). You also can't stop users to create tables or indexes in RBS tablespace, unles you revoke them quota on that tablespace!
So as far as Oracle is concerned, RBS is just the same as any other tablespace. The only tablespace that is special is temporary tablespace if it was created as TEMPORARY. So there is nothing to stop you from coalescing RBS tablespace.
But I would not recomend you to do so, unless you have rolback segments of different extent sizes (which you shouldn't have in the first place). If all rollback's extents are equaly sized, the more the tablespace is "fragmented", the less work the system have to do when it have to extend a rollback segment. If you coalesce the RBS tablespace, the performance won't improve, it will degrade. Although this degradation in performance will be so minimal that noone will ever notice....
Jurij Modic ASCII a stupid question, get a stupid ANSI
24 hours in a day .... 24 beer in a case .... coincidence?