There is only one way to hook up a 50a plug at the pedestal. The rv panel distributes the power into two 120v circuits. So unless someone has tinkered with the rv breaker box, you’ll only get 120v on each leg and not 240v collectively.
On the other hand, if someone wires a 30a pedestal as 240v instead of 120v, you can fry your appliances with the extra hot that is supposed to be a neutral.
no one calls it " 50amp, dual 120v legs of out-of-phase power".... so in proper terms, a 50a pedestal DOES supply "240v split phase power", which is sometimes called single phase, but single phase is technically a 120v term, as there is only a single phase, where as 240v has 2 phases that can be split, or used together, as the devices require...
without special uncommon equipment, there is no way to get 240v on a single wire....
a 50amp RV circuit is simply a 240v circuit with a neutral added so that the legs can be "split" and used individually as (2) 120v legs, but if you wanted to connect a welder or other 240v device up to it, it will work just perfect..
but its how the 240v circuit with the neutral wire, connects into the "specific" distribution panel which determines what you get out of the outlets... commonly used in america are 120v panels, 240v panels, and 3 phase panels, which are all arraigned/assembled differently inside to handle and distribute the power as desired.
if you had a 240v appliance in the rv, (some do) you wouldnt need a different power post or cord going into the trailer, but you would need the same 50a service, AND a distribution panel to utilize the 240v power that the cord is bringing in.
240v power does not require a neutral or a ground to operate properly, but only the 2 legs of out-of-phase power.... north american standards call for a 3rd wire in the circuit to be used as a "case ground" to prevent electrical shock in the event of an insulation failure in the wiring or device.
RV plugs and receptacles are different than home/shop plugs and receptacles are due to the need for the neutral wire, and even though they are commonly called "50a RV plugs", they are used in other applications as well.
50a RV service is more difficult to understand than the simple home wiring, and it can only be properly understood if one has an understanding of how 120 and 240 "home" power works.... its the same but with an extra wire, and different in how the power is distributed within the specific RV distribution panel inside the RV.