For what it's worth, my cleaner shrimp (Bonaparte) has been going strong for over 9 months. I got him early last summer and he's been eating flake food for most of that time.
I have six green chromis, a handful of assorted snails and some hermit crabs. I have been using the Ocean Nutrition "Formula Two" almost exclusively since the beginning. Only within the last month or so have I begun augmenting my feedings with New Life Spectrum "Marine Formula" pellets. I just add a pinch to some of the flakes and add a squirt or two at a time to my mjMOD which disperses the food to every corner of my tank instantly.
The shrimp doesn't even have to fight the chromis (who have quite the voracious appetite) for the food. It's really cool too; you can see the green color of the flake food in his translucent belly.
This past weekend I bought a pair of perculas and a Sebae anemone so I have begun augmenting brine shrimp into the feeding, but I haven't noticed the cleaner shrimp's reaction, he still seems to prefer the flake food and an occasional pellet.
He's molted a good half dozen times since I got him last summer, so I figure whatever he's eating he's good and healthy. Also, I just recently noticed that I can tell when he's going to molt by looking at his antennae; they get sort of mottled looking (almost like he's sporting algae growth on them) right before he looses his outer skin.
Hope that helps, here's a pic in case anyone is interested:
"Bonaparte"