Dungeon cards can be used repeatedly without being discarded.
When adventurer cards are played on the dungeon card slot on the battlemat can they also be used repeatedly?
Along those lines, when cards say "weapon cards" can be doubled or bought for a discount, does this apply to adventurer cards, which have a weapon card icon, and can be slotted as weapons?
The answer to both questions is "no." The little yellow text near the top of the card determines its card type. While an adventurer can be slotted in those spots, that doesn't mean it changes its type.