Can s90 seats be fitted to S60

[IMAY2023]

Anyone know if the seats need a wake signal from the canbus system to work?

It's not wake signal, It's the ignition position 1 or door unlocked / opened signal.  I can send you trace of the all messages when ignition is in position 1 of my s60 2019. If your seats from an SPA car, one of them should trigger the seat controller module to send turn on LIN signal to the seat controllers.