50 amp service - is RV service wiring the same as others?

Actually, a 50 AMP 240 volt 4 WIRE circuit is what a "50 amp RV" needs to operate. 240 volts is only the potential difference (voltage) between both of the 120 volt legs. Most welders utilize a 50 amp 3 wire circuit--that is, they omit the neutral (grounded) conductor. The grounding conductor (notice the difference in spelling) is NOT the same as a grounded conductor. Will it work? Yes. Can it be dangerous? Yes, it the neutral is lost at the panel--it's called an open neutral.