Poacher's Mark and Facebreaker's

Does the added physical damage on Poacher's Mark apply the multiplier from Facebreaker's?

I would like to know too. I think it should work but im not 100% sure.

Yes, of course.

Each character has a base physical damage. Wikia states it's around 2-5 for most characters, with the pinnacle being 2-8 from Marauder, but it's not clear if this value counts the bonus from Strenght. Point is, differently from other games (say, Grim Dawn), your character's unarmed attack do have a base damage, physical.

Anything that increases your flat physical damage, from the implicit of an Iron Ring, to the bonus given from an Abyssus, will add itself to this base physical damage. Same goes for anything that adds to your attack a flat damage (for example, Prismweave) Quivers' bonus will apply too, so long they clearly states it applies to general attacks. For example, a quiver with "Adds 10 to 20 physical damage (to attacks)" will work, but a "Adds 10 to 20 physical damage to attacks with bows" will not.

Skills that adds a flat damage to hits against affected enemies (like Despair or Poacher) will add to your attacks.

Facebreaker's multiplier is "more", which means will kick in after the "Increased" value. Usually, you will want to stack up as much flat physical damage as possible, rather than focus on stacking up as much IncPhysDamage as possible.