No, the distributed modules all use OpenSeadragon as the default viewer. Universal Viewer is added as a module (https://github.com/Daniel-KM/Omeka-S-module-UniversalViewer). I believe UV was initially distributed as part of the IIIF Server module but then the two were separated.
FWIW, I’m still trying to get UV to work with an external IIIF image server but haven’t visited the latest docs.
I’m on OS X but running Omeka-S under Vagrant (emulating Ubuntu Linux). In planning to clone my Vagrant Omeka-S instance and doing a beta version 4 update then I’ll get right back to UV and IIIF server.