I would say ladder no. It just seems like the angled or horizontal force would be trying to pull it off. I'm no engineer but that one seems iffy.
Seat belt bolts absolutely. Those are designed to take the force of holding a human being in place in a high speed collision.
Where do you mean hanging from inside on the PH latches? If you mean the flat bar with holes that the hooks go in then definitely not. Those will bend. You could hook on to the steel structure in the PH though I bet. I've hooked a come along to it in various places to adjust springs and that's a ton of force.