Pretty good, especially if the flame was in the tank first. If so, it's probably used to you feeding. Many hawks seem to recognize their feeder, and either watch or actually swim to the water's surface when they approach the tank. If you drop in something that looks like food, it will probably try to eat it. Most shrimps look like food to hawkfish. A peppermint shrimp would be an expensive snack- personally, I prefer using ghost shrimp.
Even if the hawk gets added after the shrimp, there's a good shot it will eat it. Some people have had success keeping peppermint or other shrimp with flame hawks, but it's always a risk.