A re-gurge is unlikely when both are taken pretty close together, but the trouble is, you never know how long before the second prey item goes down, & pinkies digest really fast. Also, if they don't take the second item, at least you didn't waste the better meal item.
Snakes may regurgitate when they've just digested something & haven't yet replenished their digestive fluids- & there isn't enough to digest the second item. You never want to add an item to their meal if it's been longer than 30-60 minutes (roughly), just to be on the safe side.