Even though this futures trading will be gambling on the future prices of BTC without actually participating or using BTC at all, it will still affect the BTC market.

If the futures price is higher than the normal price, people will eventually buy BTC on different exchanges where the price is cheaper, so the prices will join together.   The same could happen the other way around.

It might take a bit longer than normal, but futures contracts make it a lot easier for whales to manipulate the market.