I don't see why not. I assume you mean to read the analog voltage with the Arduino ADC. In this case the comparator isn't needed. I don't remember the details of the circuit... But maybe, depending on the Arduino analog input's impedance a buffer can help. May not be necessary though.
You stated that "anything's gonna work" about the choice of the opamp. That's far from true. Lots of opamps cannot work based on this schematic with a single supply voltage. You should also talk about the short life span of copper probes in humid soil which makes your sensor useless.
