Reverse polarity is only a problem when you want to switch something off to work on something.For normal operation nothing changes.After all alternating current is exactly that - it changes polarity 50 times a second.In the UK I would definitely expect the hook-up to be standard mains lead - abroad you might find some reverse polarity on the same type, or more rarely now the old continental 2 pin. Not sure what is a 'euro pitch' - the website lists 4 types - basic, tent, electric, and super, so maybe the 'euro' is a version of the super pitch where you would expect to have individual drainage and water point as well as electric.
...Note that 2-pin Schuko plugs will usually only fit one way round in the outlet, so rotating the plug 180deg is of no use.
As Dometic and Thetford fridges are widely installed in Continental-European-built caravans and motorhomes that will be used in countries where the polarity of the mains power-supply is completely unpredictable, the fridges OUGHT to be immune to RP.