Why are these 0Ω resistances for?
It's an evaluation board for the chip, so they will often add footprints to allow the engineer to experiment with component values. If you look at evaluation boards, quite often there is space for extra decoupling caps, resistors, etc.
The purpose of an evaluation board is not just to watch the chip work, but to experiment on it and try stuff.
In this case, you could desolder the 0R resistors in series with the FET sources and put in low value resistors instead, then use a differential probe to measure the voltage across these resistors if you're interested in the current waveform.
I've done that on prototypes. For example, how much current does that chip actually use? To answer this question, when doing the prototype PCB layout, just put a resistor in the power supply before the decoupling cap, and measure voltage across it. When done, remove the resistor and short the pads. This is much easier to do if there is a footprint on the PCB.
Another use could be to tune the response of this ultrasound driver by changing resistor values. R33 is an example of this.