augeus providers does not support EL8. There seemed to be big changes for el8 to grub files ...
how ever simp_grub only sets the grub password and this does not appear to have changed so the old augeus stuff might work.
Set the grub password on an EL8 system using simp_grub and then see if it actually worked by booting up entering grub.
Was able to verify with a EL8 client managed by an EL7 SIMP 6.5.0-Alpha server