FriendlyHopper is a plug and play simple plugin preventing some griefing scenarios with hoppers and droppers. It hooks into Lockette, LWC, ChestShop and WorldGuard, prevents placing hoppers and droppers next to inventory-holding blocks like chests if the player may not access that block. Further it prevents crafting hopper-minecarts and interacting with blocks with a hopper-minecart in hand. Dispensing hopper-minecarts is also prevented.
No commands, no configuration, no permissions. Since checking for protection is delegated to the other plugins those might allow bypasses for ops or players with bypass permissions.
It has been in use for a while on a couple of servers, i still recommend to test it out on your server with your specific plugins etc.
Source code: https://github.com/asofold/FriendlyHopper