Preservative-treated round poles achieve a high level of protection. The easily treatable sapwood provides a continuous band of treated wood around the heartwood core, heartwood being less easy to fully penetrate with preservative. There is some evidence to suggest that concrete encasement retains moisture at the concrete/timber interface and thus creates an increased risk of decay. However, it is not considered a significant risk in the case of CCA-treated softwood.

The cladding installation details on the WoodSolutions website are intended to be generic, ie. applicable to all types of timber cladding.  By clicking on the "Installation" tab you will find details of recommended fixings, but they are not specific to American red oak. We are not qualified to advise you on warranty issues and are not sure what warranty your supplier has offered, if any. It would seem that if the supplier has referred you to the WoodSolutions installation guide then they have adopted that as their product guide.

We consider the advice that "the tongue and groove are brought tightly together by using a ch

A reference in our library (CSIRO Division of Building Research Special Report, Low-Rise Domestic and Similar Framed Structures Part 5) makes the point that in the case of strip flooring "the concentrated loading is the critical design consideration....not the uniformly distributed load".

We assume the pergola won't have a roof in which case oregon isn't highly recommended for weather exposure. Australian Standard 5604, Timber - Natural durability ratings, places oregon in Durability Class 4 with a "probable" above-ground life expectancy of up to 7 years. A paint coating may prolong the life of the timber if well maintained on all surfaces, but if the paint breaks down, allowing water to become trapped under the coating, it can have the reverse effect of hastening deterioration.