I usually play PS02 through the Steam launcher, and I have no issues playing the game with my PS4 controller. However, my controller does not seem to be supported in the beta. (driver tests show all the buttons recognized and functioning properly outside of the beta.)
Normally, I'd just switch to keyboard/mouse. However, I don't use a mouse, I use a Wacom stylus/tablet, instead, and it just makes the camera spin around me wildly, without any way to control it smoothly.
The game is currently unplayable for me to test.