This is the first time i have run into this in my career, or atleast that I can remember, I scan both enhanced and global and I find no pids for the downstream o2 sensors.
I am looking right at them. I can only think of recommending a software flash unless someone has seen this before.
Have you tried more than 1 scan tool?
Does the oxygen sensor monitor show as unavailable by chance? My guess is it has an aftermarket "performance" reflash. Many of them eliminate data for the downstream sensor and alter the monitor. A PMI on the IDS without doing the inhale will fix the software, but then you may have a bunch of codes depending on what was modified on the car.
Only time I have seen that is when the vehicle is tuned.
In that case I would have to agree with others who said it likely has a custom tuner flash in it.
I would try to flash it back to a stock configuration but caution the customer that all bets are off because of the non standard modifications.
If you were going to delete the downstream O2 sensor on a sports car the motivation would most likely be to remove the catalyst without causing a MIL for the cat monitor. I'm not familiar with the vehicle but check the cat out. Light rap with rubber mallet - Anyone in there?
I think there are some rare cases where a monitor is not required to be implemented on a specific vehicle but I don't think that ever applies to the O2s. Would be interesting to see if it failed a standard emissions inspection device.
Randy Berklau would be a good guy to ask about this.