Using an SSR photoelectric sensor with Arduino
Thanks for the responses to my question. I'm answering my own question because I was able to do some further research into this specific unit. Instead of getting limited answers through the vendor's tech support, I eventually found Eaton, the company that produces this item, and spoke to their extremely helpful sensor tech support person.

So the basic answer is yes, powered separately, the unit can be used with an Arduino. I should've clarified better that I was mainly concerned about using an Arduino with the unit's outputs. He confirmed that the unit's outputs are isolated from the power supply and can work with either AC or DC, so no conversion to DC is necessary. The outputs function as a switch contact whose state the Arduino could read directly. That said, tech support did still recommend the mechanical relay version as another user pointed out. Despite isolation on the outputs, there could be some current leakage with an SSR, whereas there shouldn't be any with the mechanical relay version, and my application is not a super-high-processing environment where a mechanical version would soon fail from wear and tear on the physical contacts (using the example he gave, not a UPS shipping facility where they would need a much longer-lasting SSR-version sensor to count tens of thousands of packages a shift).