If I have a dynamic provisioner that is a long running bash script, does

pulumi up

wait until it's finished? If not, what's the best way to track progress of this script?

By dynamic provisioner do you mean using the pulumi command package or a python dynamic provider?

I realised after I posted I meant command and I think the answer is no

The command package will wait until your script has finished running. If you need to ensure that the resource is really created and available you need to add that wait logic to your script.