Well 9mm since you'd like a real answer and not the normal internet uninformed I'd suggest you ask one of the ammo companies...send 'em an email. I know they're busy nowdays but with all the profit they're making they should be polite and answer a sensible question like yours.
And now playing the role of the internet uninformed I can personally assure you dessicant will not harm ammunition, it really does take the moisture out of the air and does not remove the air and gunpowder burns just fine in space because it chemically supplies its own oxidizer (air).
And goodness...we haven't had a 'guns in space' thread in weeks and weeks. Almost as long as 'guns and bears' and 'guns and snakes'. (And that's okay with me.)