From what I understand, in dens you stake a single token instead of a liquidity pair and still earn CUB as interest, so you won't suffer impermanent loss as you would when providing liquidity.

Re #2: it's not zero. Your provided liquidity is there. You can check it using this tool https://howmuchismylp.com/

Use MasterChef Address: "0x227e79C83065edB8B954848c46ca50b96CB33E16"

Hope it helps. I'd let the experts explain deeper. 😊
-@arrliinn