What is the difference between the ILV pool and the ILV/ETH pool?

The major differences are what you stake into the pool, the pool weight, and the risk.

With the ILV pool, you stake ILV. With the ILV/ETH pool, you first provide liquidity to the Sushi ILV/ETH pool and receive SLP tokens in exchange. You then stake those SLP tokens.

The ILV/ETH pool receives a larger percentage of the dispersed tokens. By providing liquidity you are increasing the total liquidity in the pool, which has the positive benefit of lowering the slippage when someone purchases from the Sushi pool. In order to somewhat mitigate the risk of Impermanent Loss, you also earn a percentage of the exchange fees from the Sushi pool.