Fire shrimp tend to stick in one area of the tank, likewise with scarlet cleaner. As long as they never make contact (which is surprisingly unlikely as even during feeding my fire barly comes out), they should be fine. My scarlet cleaner gets along just fine with my fire shrimp as long as they keep their distance (which isn't exactly that far from each other's cleaning stations).
IME, fire shrimp are extremely reclusive.. I often forget he even exist in the tank until I notice his antennas maybe once a week/month. They're pretty but getting to catch one in the open is a miracle and sight to see which is pretty disappointing on my end.