Aren't cap dumps in essence negative value?
Really depends on the rest of the deal. If Bouma as a cap dump were just to be tacked onto a trade for a far better player, I see it as more of a no net value sort of thing - the other team would get an NHLer essentially for free, but lose the salary they'd otherwise have to sign another NHLer of basically his same calibre - they give up nothing for something that's about as good as it is bad.
If the swap were just bottom six guys and Bouma is a key part of the deal, then yeah, he likely has negative value and we have to add a fifth or something to make up for the contract.
Overall his contract makes him difficult to trade, but I hadn't ever figured management would try to trade Bouma because of the small amount of takers. You raise a good point though