I think you're raiding 25m? If so, then you should have plenty of raid cooldowns for the swellings, no one should be dying to swelling+debuff ticks. Dispell people who are not full hp prior to swelling and sure, shield them, but the raid cd's should cover most of the damage.

BTW we just stack up behind the boss and only move for prisons, if you do it the "1 group at each prison" tactic, then yeah you might just have to dispell even without the buff, just keep an eye on your corruption, and shield the people you can't dispell before swelling.