I know it is intended for some spawn eggs to be unusable, but this is different!
First give yourself an unusable spawn egg like a giant spawn egg with the command '/give @p minecraft:spawn_egg 1 0 {EntityTag:{id:"Giant"}}'. Then place it in a dispenser. Activate the dispenser with redstone and as intended no giant will spawn BUT the spawn egg will disappear anyway.
the egg still get's used, but the egg just says nothing to spawn, that's intended