Maybe I can attack this from a different angle.
Is there a way to get the calc info from the WF properties somehow? If I can get the name of the DM step (which is in the Filter field), I'm pretty sure I can figure out how to query the status. There's a snippet for GetUserWorkflowInitInfo that seems expose a lot of properties but it will take me a while to dig through everything that gives me.
Provided I can get what I need from there, the next step is figuring out how to check for running Task Activity by that name. This is where the visibility seems to break down even further. The only ways I can see to interface with the Task Activity seems to require knowing the task activity ID in advance/being inside the DM job already and accessing it through the args. Maybe I'm missing something here as well though.
Worst case, because it's not at all dynamic, is just querying the task activity table directly for a task with that name and running the query every 30 seconds or so until the status shows complete. It's gross but it will work if there are no better methods.