Were RERAs measured in your sleep study? If not, you should probably get another sleep study at a sleep lab that measures RERAs, so as to get a definitive diagnosis of whether you have UARS. (You could call Stanford Sleep Medicine Center to ask if they can recommend a sleep lab in your area for this purpose.)
Yes, an oral appliance can be effective for treating UARS. (But an oral appliance is usually not a good idea if there is any degree of TMJ joint problems.)