No one can guarantee the actions of every individual fish, but IME, skirt tetras are fin nippers, especially in regards to large-finned and slow moving fish like angels.
I prefer to be safe rather than sorry but that's just me!
As Biscato33 suggests, peaceful Bleeding heart tetras are usually fine with angelfish, but they do grow quite large and a school would probably overcrowd your tank especially since it's a hex tank. I would NOT put a dwarf gourami in there.
Hex tanks are designed more for people than for the fish. Horizontal room is what's needed - especially for schooling fish like tetras and bottom dwellers - since fish don't swim up and down.