Credit goes to filament
for pointing this out over at the gildor forums,
UModel can't export and convert the audio files automatically, but it can save them in .uexp+.ubulk format. That's not playable normally.
The fabulous bnnm over at hcs64.com recently developed a decoder for the UE4OPUS format and included it in his software, vgmstream. It can convert .ue4opus to .wav.
To obtain a supported .ue4opus file from the .uexp+.ubulk files saved by UModel, you need to use a certain script also developed by bnnm.
Visit https://hcs64.com/mboard/forumlong.php?showthread=56732&lastpage to grab the .bms script. You can apply it to .uexp+.ubulk using QuickBMS to get a .ue4opus file that you can convert with vgmstream to .wav.
I've created a zip of the required files to do the conversion, Blenux Mega Download LinkBrief How To:
Save Opus sound uasset with uModel (or QuickBMS should work also).
Open QuickBMS with extracter.bms
Select ubulk of saved Opus sound
Place ue4opus onto test in vgmstream folder
You now have the wav version of that file.