The Hughes XH-28 was ordered in 1952 with a possible first flight date in October 1956. So, considering your reference is from 1956 I doubt there is that connection.
As far as the Piasecki PA-1 is concerned, a Piasecki document that I have describes it as: "..... heavy lift VTOL studies were performed for the Army including the movement of a 50 ton tank externally. A matrix of rotor/propulsion systems studies showed multiple shaft driven rotors were the optimum heavy lift configuration for the near term and a blade mounted turbo-jet system (PA-1) for the long term. The high development cost of the latter unfortunately dissuaded any further research effort."
The document does not have an illustration of he PA-1.
At about this time Piasecki had moved on from helicopters to VTOL aircraft.
As far as Flettner is concerned, as far as I know (from Dana Bells Directory of Airplanes and some other books, Flettner is a pre WWII German company. So somehow I fail to see how they can be considered to make large helicopters for the US Army in 1956. But may be I have missed something. Would not be the first time.

To be quite honest, some of these little snippets from old Air Pictorials seem to be rather irrelevant to the work we do, but that is just my opinions, for what it is worth.