1-2% of the money raised is not so much and bounty participants deserve that. Also, it can cause more investors to attract. Because they are no longer worry about the price fall after bounties are paid.
It is true that if bounty hunters will be paid ethereum for their work, there's a slight chance that bounty hunters dumping tokens will greatly affect the market value of the token once it is distributed. However, we should also keep in mind that a token will only have a market value once it has a high amount of volume, and there are some ICOs that do not gather enough funds to fully develop their project or even market their project because of lack of fund, that is why they choose to pay with their token.