Using joist hangers to support a lean-to/skillion roof?
Joist hangers are fine for this application. You'd want to notch the ends of the joists with a level cut so they rest properly in the hanger. 

However, the blocks are a bit hokey. It's not great to hold things up with nails in shear like that with such small pieces. it would be better to simply put a ledger across the wall at joist height.