On my way home I stopped at a KOA for the night and got a pull through site. I have a digital readout, Surge Guard. Within a few seconds of plugging it in to the shore power, it indicated an open ground and shut off power to my trailer, although I hadn't plugged that in yet. This occured on both 30 and 50 amp circuits. So I went to the office to report it and they gave me another site, the which of was fine.
You don't want to be in an open ground situation. The risk is possible fire or even electocution. Without a ground for the electric to flow into, it could possibly energize your rig and if you touch any metal, you become the ground. Not that it will happen, but the risk is there. So, if you don't have a Surge Protector, get one. You never know what's lurking in those power pedistals. Others on here can share experiences with theirs as well.