Ceiling mounted punching bag without compromising structure or floor above
Hanging a 100lb weight from a joist should be no different (structurally) than putting a 100lb weight on top of the joist.  So since a 200lb person can easily stand on the floor above the joist, just hanging a 100lb bag from it shouldn't cause any issues.

The larger issue here is going to be what happens when you actually use the bag.  Speaking from experience, it's going to be similar to having a bunch of kids running around the house - things will shake and rattle a bit, and over time you might get some cracks in plaster/drywall, but it shouldn't cause any structural issues.

ETA: I missed the part where you mentioned using a mount that absorbs a lot of the shock from use.  If that's the case, then you can probably ignore my second paragraph.