I was going to use an AX500 channel for a high-side (Voltage Source) and a low-side (Voltage Sink) dimmer control. After probing the outputs it appears that the AX500 is PWMing the low-side FETs and switching the high-side FETs. Is this true?
That is correct.
The driver used on the ax500 has a very slow high side switch. So the high side stays on and the low side pulses.
All our other models work the other way around.