I thought the main problem with the 'noids running on CO2 is the theory that the small o-rings inside the noid absorb CO2 and swell, causing the noid to sieze.
The same is said about the front noid on Raceguns (basically the same noid as in an LCD Angel) , but I ran mine on CO2 for 50,000 shots and have suffered no ill effects.
I also ran an LCD on co2 for one game a couple of years ago, can't remember why - no air available or summat, but it got flippin chilly