Is it possible to hide an object from certain cameras?

It's common practice in many first person shooters to have a separate 3d model for the arms and weapon that the player sees, versus what other players in the game see when they look at him.

For example, in a Halo 3 multiplayer match, the weapon you see from the first person perspective is a very detailed version of the weapon you are holding, as well as a set of arms holding the weapon with detailed weapon reload animations.

However, what other players in the match see when they look at you is a less detailed version of the weapon attached to your player models hands, along with a less detailed reload animation than the one you see from first person.

How would you accomplish something like this in Unity?

Use layers:

http://unity3d.com/support/documentation/Components/Layers.html