Roughly speaking:
Poser skeleton = Blender's skeleton
Poser rigging = Blender's envelopes
Poser morphs = Blender's shape keys
Poser ERC = Blender's Driven IPO's

Poser rigging works on clothes semi-automatically by applying the same (or a similar) skeleton+envelopes to the clothes geometry. This is not automatic for the clothes creator. You can try the same thing in Blender by using envelopes for rigging and applying the armature to the character and the clothes. However if you rigged your character with weight painting you can re-use the armature on the clothes but have to weight paint them separately.

Poser morphs also working in a face mask is done by ERC. This is not automatic for the mask creator. The morph has to be added to the mask and one channel has to be set up as driven by the other by editing the Poser pz2.

In Blender you set up your shape keys in the character's face and another in the mask and make the mask key a driven IPO. This is easier in Blender than in Poser.