I have a 125g reef tank, I have 2 scarlet cleaners, and 2 fire shrimp. They have their own spots on opposite sides of the tank. The scarlet cleaners tend to roam a lot more than the fire shrimp. All four have been with me for over 2 years.
I will say though that the fire shrimp are very secretive, and tend to hide a lot. But when food is introduced into the tank they come out to get their share. They do clean the fish, but the fish have to go to them. Which a few have learned to go to them.
The scarlets are more out in the open, and will intice the fish to them with their antenae. I have large fish, so they are open to their inticement.
As far as getting along.....let's just say that they tolerate each other. The fire shrimp tend to be the aggressor. They will hunt the scarlets down to get their food. I feed shrimp pellets, LOL, and make sure to feed each territory.
They are really a joy to have in the tank. It is a shame though that the fire shrimp costs so much and hides most of the time.
Just be sure to acclimate the shrimp for a lot longer time than fish, they are very sensitive to changes in ph, and salinity.