nfortunately, no... The muffler pressure is related to both RPM and throttle opening. If in my helicopter with the gasser (electronically governed) pitch is added, the governor opens the throttle and the muffler pressure rises significantly, despite RPM remaining constant.
And then again it also is depending on mixture strength: For the same RPM and same throttle opening, if mixture is varied, muffler pressure also changes.

Under normal conditions that really is not a big issue, BUT it means you cannot just make a bunch of full throttle testruns with different propsizes (to alter RPM) and take muffler pressure readings and base an entire mapping on that. That measrement would be useful to determine the relation between (all else remaining unchanged) RPM and muffler pressure, and assume that that relation remains the same for other throttle openings

Or do you mean, that the pump is actually controlled by a sensor determining actual muffler pressure in a practical set-up? Yes, that would be exactly identical to real muffler pressure. But it would defeat the purpose of the system a bit, because then a craptrap is going to be a whole lot easier for most people.