I normally see some crypto projects which promise Investors certain amount of dividend depending on how much coin/token they own.
The word "Investors" is normally used for people who own shares of a particular project/company, but in cryptocurrency this "shares" normally refers to coins/tokens, which makes me wonder if bounty/airdrop hunters are also considered "Investors" since they hold certain quantity of these coins/token
Yes they are, if you are holding any of the coins of a project that makes you an investor in it. You do not have to put in money into a project for you to be considered an investor. You just have to put in your time and effort when it comes to bounty and that is a good an investment as putting money into it, so year bounty hunters are investors too.