It seems that even in the official UE4 Oculus Audio can't be selected under Android audio settings. It seems that it just has to be set under Windows for it to work also when building to Android (at least it seems that the Oculus Audio plugin source is already setup to target Android at build time).
I'm actually not sure anymore if Oculus Audio works for the Quest and Unreal Engine. As I posted here https://forums.oculusvr.com/developer/discussion/81809/some-clarification-please-oculus-audio-and-un... (also forwarded to Oculus via the support direct contact), I'm not sure if the spatialization I'm hearing is being done by Oculus Audio or by the builtin spatializer. I got to compare with how it sounds on the Quest using Unity and the spatial image is certainly much more accurate than in UE4, which leads me to think it's using the internal spatializer. Still zero response from Oculus to confirm this (including the lack of 64 bits LibOVRAudio when they are requesting users to not submit 32 bit builds to their store). It is often frustrating to see that UE4 is second class citizen as compared with all the support and prompt updates that Unity gets.