To have Haoushoku Haki, one must have the ambition to be a ruler and have the determination strong enough to achieve it.
I don't think any Marines would have it, because they are all controlled by the World Government. If any marine had Haoushoku, he would have staged a coup d'etat on the World Government or something.
If anything, the admirals would have powerful 'military' Haki, the Haki of a leader and war veteran. Great military leaders need to look and be powerful to boost the morale of men and their reputation from their victories send fear to the enemy.
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