This sounds like a bit of fear-mongering to me.  We've been thru quite a few dry/droughty years here in the last 25+ years. I've never seen a reduction in soybean nodulation based on the previous year's weather.   I will also say..... most of the time when we have a droughty summer, we also get fall rains. So, that may help mitigate the situation.  I don't know what you guys in the mid-west are seeing now - are you still very dry, or are you getting some rain showers?  My guess would be that if you get close to normal fall rain showers, you will be fine.  This will be a "non-issue".