I collected some data on this a while ago. Snatch does appear to slightly increase the number of chests that drop. For example, I observed a 10-15% increase in bronze chest drops in Ultimate difficulty for an early Advent event with ~5 stacks of Snatch. In general, I'd only recommend it for full-auto setups that can clear >90% of the time. Applying the stacks is just a waste of time otherwise. Even better, use a team equipped with a full loadout of R accessories with the drop rate up trait. That should give an equivalent effect.