Can you use a 3.5mm jack splitter to combine the audio and mic cables from a headset into one socket for it to then be used with a dualshock4 control?

No, a 3.5mm jack splitter cannot effectively combine the audio and mic cables from a headset into one socket for use with a DualShock 4 controller. The controller requires a specific type of adapter that separates the microphone and audio signals correctly. A simple splitter won't provide the necessary functionality for both audio output and microphone input to work simultaneously.