What is wrong with dialling up 1013.2 on the altimeter and reading the PA straight off the most accurate instrument, then read off the oat gauge (note spelling) and apply 120' per degree difference from ICAO to give you a very accurate DA. It rather sounds like things have got too complicated in the civvy world, probably to help operators squeeze the last hour of flying out of a shagged engine.
The wet bulb temperature is not a dew point indicator - it shows the lowest temperature that the air can be cooled to by evaporation, which is not the same thing.