Won't work out of the box I'm sure!
The grasp message is part of the list of possible_grasps you give to a pick actionserver call. I'm still not very clear how these grasps are evaluated by the pipeline. (If someone could give a hint on this I would gladly read it!)
What I can tell you from it's fields (other than it's descriptions on the message):
The frame_id I'm using for this PoseStamped is my base_link of my robot.
The allowed objects here can touch the gripper link in the approach and closing the gripper moments I think (as of my empirical tests in simulation). This is bad in my case as I'm crashing a finger of my gripper (a hand) sometimes when approaching the object... but this seems correct as I'm allowing explicitly to touch! Here is where I would like to know how this is evaluated by the pipeline.
Sorry about this bunch of random information but it may be useful for someone (or someone may correct me).