Can't imagine it would do any harm as the refrigerant system is sealed. I've even heard of this being a fix on some caravan fridges if they start running poorly.
http://caravanchannel.proboards.com/thread/4306/fridge-working-turn-upside
I use a small portable freezer in the caravan, in addition to the onboard fridge, and found it upside down on the caravan floor one year when we got to Scotland after a securing strap broke and it fell off the bench seat. Looked at the instruction book and all it advised was letting the unit sit for a couple of hours after transportation to allow the refrigerant to settle. Switched it on later and it was fine and has been fine since.