Energy blocks get done OTC. Interest rate blocks usually get done as OTC depending upon the particulars of the swap construction. The OTC brokers typically have their customers on a dedicated land line (squawk) and/or an IM system. Counterparties need to be ISDA listed or have the trades run through Clearport or ICE depending upon the flavor. For bilateral trades the counterparties typically have 'bonafides' on file with each other which includes contractual agreements (think liens or promissory notes) and lines of credit. That is all.
The REG NMS doesn't protect anything. I still see trades going off above and below NBBO. It's all a hoax..
RegNMS protects top-of-book quotes during RTH only. You can easily take the best bids on all 11 market centers and send the rest down to NYSE sweeping the book down $1 if you want to.
No. A delta neutral trade (prefectly hedged trade) can be priced outside of the (N)BBO; i.e. multilegged option trades tied with Stocks.
No, it is not true. Your statement is only true in a general sense. The rule has very many different exceptions allowing trades to be executed outside the NBBO. You should find the SEC site, find the rule on that site, and study it.