WAAS (and other SBAS constellations) are used for RNAV/RNP LPV approaches indeed (for both lateral and vertical navigation), but WAAS is only used to obtain atmospheric corrections for the GPS signals, the WAAS ground stations do not transmit atmospheric pressure. Furthermore, unlike GBAS (Ground Based Augmentation Systems), SBAS ground stations are not located at the airport, they can be dozens or hundreds of kms away making the atmospheric pressure from there not very useful.

Good article on the topic by Airbus: https://aircraft.airbus.com/en/newsroom/news/2022-06-satelli...