It would be nice if there would be volunteer to create Breeze icon theme for YaST2 to look more consistent in KDE Plasma 5 if Breeze icons for desktop selected. See also discussion in https://lists.opensuse.org/opensuse-factory/2017-02/msg00227.html
Note, Oxygen icon theme still exist (and still complete), it was just no longer used since around openSUSE 13.2 version. But now yast-theme 3.2.2 source package is fixed to again provide yast2-branding-openSUSE-Oxygen package to switch into Oxygen icon. Same mechanism could be provided for Breeze icon theme.