It doesn't get any better even at the umpteenth explaining. Witnesses surviving or not simply don't have anything to do with the ability to see into a Breen suit, if the Breen evaporate - it's an element Worf should never introduce into the dialogue if he believed in evaporation. Yet Worf does bring it up, as his premier
explanation to why he can't tell Ezri whether the Breen are fuzzy, even. It can't be read as an incidental
bit touching upon an already clear-cut issue of why the Breen faces remain hidden.
At the very best, the dodge of Worf "knowing Breen evaporate" amounts to the same thing as the Borg not being known to the Federation after "Regeneration" being okay because they didn't technically give their name to Archer in the episode... It just doesn't explain anything plausibly, it merely dodges.