can The death aura be used by minions?
If I use a minion gem in death's oath my minion can have the same aura?
If not, Is there another way to do this?
The "Grants Level 20 Death Aura Skill" behaves as a skill gem the same way a typical gem like Cyclone or Fireball does. You cannot "give" a minion skill gems by linking them together but it means you can support Death Aura with support gems as seen under mechanics on its wiki page.