I am guessing you are referring to something like this... This one is available from pplmotorhomes
The first thing I notice is one of your 50A legs on the trailer side will have only a 30A capacity and the other 50A leg will have a 15/20AMP capacity. I also always worry about having a MALE connector out in the open that may be a safety issue in some instances causing a shock hazard. When you plug in the one side into the camp ground pedestal the other side of the male adapter is out in the open until you plug it in. It does not appear this adapter will have open HOT male connectors but just something to respect in case something is wired wrong inside the trailer.
Using this drawing from DMBRUSS showing where two 30A sources are connected to a 50AMP connector shows this same Scenario if one of the 30A connectors is substituted by a 15/20AMP connector...
The 50A side of this box would feed the two 50A Distribution Panel sides as shown here in this typical diagram
Other than GFCI issues mentioned above I don't see why this wouldn't work.
I would prefer having 30AMP capacity on both legs of the two 50AMP RV panel distribution and then you decide what is turned on at any given time to keep from tripping the camp ground pedestal circuit breaker.
Then I would run an extension cord to the camp ground pedestal and plug into the 15/20AMP service to run alot of things inside the Rv trailer to help with the possible overloading of the 30A service.
Be careful out there
Roy Ken