Urgh. This is another one of those "Fine if..." situations.
If the people are of good character and know what they're doing, then sure.
The problem lies in the 'average player' not really understanding the differences in power between guns, and the effects on human skin. Many people, even otherwise sensible ones, look at an airsoft pistol, subgun, AR, LMG side-by-side and directly correlate their power and accuracy to videogames.
Then there is the problem with power trippers who think that power directly equates to better.
Unfortunately we can not rely on people to be trustworthy in their knowledge or intent, so it falls upon the organizer to check and regulate everything being brought onto the field.
I personally believe that any Co2 handgun should be subject to chrono check, simply because there is so much variance between manufacturers, between guns, and even between mags in some guns (pistols which can accept both Co2 and Propane mags will chrono differently on each propellant type).
Some Co2 guns run at ~300fps (TF-11) while others run at ~470-500fps (every Dan Wesson revolver). It has to be case-by-case and people have to realize that ~350fps is still absolutely outdoor viable.
I'm going to use this space while I'm here to suggest that every game organizer institutes an outright ban on Dan Wesson revolvers unless the user is known to be reasonable and is 'sniping' with them. There is no significant drop in fps when moving to a higher weight bb, and the lowest I have seen them chrono is 460fps, even on the 4". This means that these guns can operate well over 2 joules.
If the gun has been modified to shoot under 400, be sure to test at least 10 shots. If 6 shots run 360, 2 run 350, and 2 run 460 it's still a 460fps gun.