That is, level 3 does not guarantee participation in this ido? Or does level 3 always guarantee nothing and I always participate in the lottery anyway?

There are no guaranteed allocation, since we use a lottery system. Staking will get you more POLS Power, that will increase the value of your tickets, which increases the chances of you winning an allocation. You can however guarantee yourself a whitelist spot by being among the top 10 holders of $POLS. You can check on bscscan and etherscan to know the top 10 holders.