Originally Posted by DustyGeek
I think it should work fine. The receptacle on your generator has two 120V hot legs (opposite phases), a neutral and a ground. I believe one of the hot legs on the generator plug end of the adapter is just not used since there's nowhere to connect it on the receptacle end. If you want to be absolutely sure, take a voltmeter and measure it, testing each leg against the other two. You should get 120V from hot to both neutral and ground, and nothing from ground to neutral.
Here's my No~Shock~Zone article about how to measure an outlet BEFORE plugging in your RV. RV Electrical Safety: Part III – Outlets | No~Shock~Zone
And here's a video I made on how to test a campground pedestal for proper voltage and grounding.