It says to flip the hero and place a damage token on him. In our case prisoner was Gloin. Does the damage trigger his effect and give him a resource?

I would think so, but some cards like Wilyador have text "place in staging area with 2 damage on it" already.

Gloin ''suffers'' the damage, so I would give him a resource.

Played that way too Thanks.

I think that Gloin is the only hero of the game that ''suffers'' damages instead of ''taking'' danages...