There are two main theories from what I gather ...
1) Ich is always in the system -- if the water params are good and the fish are healthy, their immune system will fight it off.
2) Ich is the devil
Us personally, we don't know which one we believe in yet ... we recently ran our tank fallow for a while, and have been QTing our fish. But a couple of friends of mine, don't QT ANYTHING and their fish have been live and healthy for many many years.
The reason I bring that up, is to pretty much say that it's really up to you... if you plan on "actually" treating the fish, then you need to get him into a QT tank (unless you've no corals and inverts). If you just want to feed it till it comes back to health, then no need do anything; just keep feeding it a lot of food.
Cleaner shrimps might help in making the fish feel better, but it's not a "solution" to ich ... also I'm not sure if all cleaner shrimp clean :-/ ... our cleaner shrimp never go close to a fish ... #@!#$%#$