I recently did some work for ITV's Dancing on Ice on my Canon C300 and thought I'd note down a few things: pluses and minuses for using the C300 for this kind of work.
For me the C300 really excels when you can control the situation you are filming. Web commercials, corporate films, traditional style documentaries or low budget films all tend to have a slower pace and the action can be stopped and repeated to ensure you have the shot. When a director from ITV called me and said he wanted to improve the look of the first episode of a new series of Dancing on Ice and liked the C300, I imagined trying to follow focus as a load of untrained celebrities careered around the ice in an uncontrolled fashion, that said, I am always up for a challenge.
Firstly, some plus points. The C300 has all of the features you would expect of a normal broadcast camera, which allows it to fit in with the rest of the cameras on a large scale shoot. For any shoot where several cameras are recording, synching them together with timecode becomes essential to the edit. A lock it box can be attached to the camera, and it has a TC in, so you can feed the camera timecode that won't drift throughout the day. The camera can be black balanced, something that the camera assistant or DIT might want to do at the start of each shoot. It is also really easy to dial in an exact colour temperature, which makes life easy matching shots in the edit.
There are always going to be a few negative points or difficulties when working with any single chip camera and the first of these is lens range. With a traditional 3 chip camera, such as the Sony XDcam, the lenses focal range is massive. Take the standard Canon HJ22 lens, it has a 22x zoom, with a flick of switch you have a doubler in, increasing that range to 44 x. By comparison, a large sensor camera, such as the C300 using the 70-200mm lens give you a range of just under 3x. You can of course put in a doubler of sorts (with a canon 2x extender) but this takes time to mount, and then you still only have a focal range of under 6x compared to 44x from the HJ22.
You could of course use a lens like the HJ22 on a C300 using an EOS to B4 mount adapter. This gives you a lot of range (although not without the doubler as it must always be in to help with the crop factor), however, the whole point of using a single chip camera like the C300 is to use nice lenses with a shallow depth of filed, so chucking a HJ22 on it, in some senses, defeats the point. I only use an HJ22 on a C300 when I really need the range. (For a more in depth look at lens ranges and crop factors see this article)
What lenses with a long range give you is an ability to quickly respond to something that is happening, be it close or far a way, if you happen to have the wrong lens on when something dramatic happens, you could miss it.
The next challenge is focusing. Shooting with a shallow depth of field, while people move around and the scene is totally unstructured is of course going to be tricky. The issue with reality style programmes is that directors are usually looking for interesting synch from whoever is on the show. Often everything that is said is recorded in it's entirety onto an audio hard drive, and APs will be noting down interesting bits of dialogue. This will inform the directors choice of which shots to use, so it is important to keep shots usable and in focus for the longest stretches of time possible.
I guess to answer to the original question, can you use the Canon C300 for reality and entertainment shows, the answer is yes. Although standard 3 chip cameras such as the XDCAM 800 are likely to be in focus for more of the time, and can access a greater range or vision, there is a trade off to be made. The C300 could potentially record less moments, but the footage it does capture is pretty stunning. I think the filmic look the camera has, the colour quality, the shallow depth of field and the large dynamic range, means the sacrifice is worth while.