They recommend DOW55 because quite frankly the tolerances might be a bit loose and they're trying to compensate for it by using the 55 to swell the o-rings. This may cause problems in marker maintenance because you may have trouble putting the same o-rings back in.
If you don't problems with leaks, you're probably ok with plain DOW33 -- or any standard "paintball grease". I got that on my G6R.
DOW55 is really intended for static installations where all the o-rings are replaced every time the device is opened/dismantled for maintenance. Makes tons of sense for expensive equipment that's opened only for yearly maintenance -- maybe not so much for paintball.