Regarding the sprayer, the question is not necessarily what happens to it when it's not spraying water... when the nozzle is in the process of spraying you, it's unavoidable that some of the contaminated splatter goes back into the nozzle.
Anyone who uses that toilet will inevitably share the germ cultures from one another's feces. That doesn't strike me as very sanitary.
You ever spray a hose away from you and get hit with the splatter? Imagine spraying the hose up to clean the underside of a gutter. Can you imagine getting hit with splatter? Can you imagine the hose getting hit with splatter? Can you imagine the rim of the nozzle getting hit with splatter?
Sure, the outside of the nozzle/arm will get by splatter, just like the rest of the toilet bowl. But the nozzle rim and interior will remain splatter free because of the jet of water. Any surface where particles can touch the stream will be washed clean by the stream.
This is no different to the splashback that can occur when poop hits the bowl water (water that's been touching the splattered sides of the bowl).
It's no grosser than a regular toilet, and your butt will be cleaner.
Meaning that cross-person fecal contamination should probably not be one of your major concerns. The nozzle does some sort of intense rinsing. I don't know about sterilization.
Anyone who uses that toilet will inevitably share the germ cultures from one another's feces. That doesn't strike me as very sanitary.