Guild Wars 2

As per title the Dragon Stand mobs that spawn during the map wide meta event do not contribute to Weapon master progression achievment.
They give xp and drop loot so this seems like an oversight.
Ambient creatures on the map do progress weapon master just not the HoT mobs.

The only way to get progress on a Weaponmaster achievement is to deliver a death blow with the weapon, inflicting the killing damage from the weapon itself. If the mob dies to a rune or sigil effect, a utility skill, a trap created by the weapon (i.e. marks), a condition inflicted by the weapon, or another player’kitten, the kill does NOT count. In DS there are usually so many players that it is rare you get the killing blow on any given mob, so you don’t get Weaponmaster progress. The reason that ambients give progress is that you can be 100% sure that they are being killed by the weapon’s direct damage.