The card provides a single combat skill for Bramble:
MIGHTY PRIESTESS: Attacking Rangers must roll at least one unmodified '6' result, or all hits rolled are blocked and ignored.
On page 22 of the published rulebook, Bramble also has a single combat skill:
Blessed by the Gods: The attacking Ranger must roll at least one unmodified 6 or all hits rolled become blocked by Bramble and are ignored.
On page 21 of the published rulebook, provides the following guidance:
There are four Leaders assaulting Last Stand, each with their own special combat skills...
And, on page 17 of those same rules, under Combat, it states:
There are three types of combat in the game; combat with Raiders, combat with Monstrosities, and combat with Leaders. Each is handled diffently.
So, IMO, the answer to your question is that the the Earther Warband combat 'skill' does NOT apply to Bramble.