I live on the Gulf Coast about a thousand miles from the nearest Toyota dealer who sells the Plug-In. Will the local Toyota dealers in my area, none of which sell the Prius Plug-In, have the training and tools to service one?
Your best bet is to just call local dealerships and ask them directly. From what I heard others mention here, the PiP is essentially the same mechanically as the regular Gen 3 liftback, aside from a bigger battery and lack of a spare tire. Worst case scenario, the techs could always call Toyota support for anything they may not know about it.
The above quote is from this thread: Buying PiP in "Non Supported State" | PriusChat The long and short is that some dealers may be better at providing service than others, and may even claim not to service them. However, the Toyota national policy is that PIPs can be serviced at any dealer. This makes sense, since there is almost no mechanical difference between a PIP and a regular Prius, including all normal maintenance.
If they can service a Prius, they can service a PiP. Worrying about warranty service is silly BEST DEAL GOING: learn the simple DIY stuff and expect to stay out of the stealership's grubby hands.