You can earn ethereum through campaigns by participating on it, like participating to a social media and signature campaigns that are offering ethereum as a payment. You just have to follow all of their rules and accomplish your job properly to be able to be paid weekly.
There's no campaign that is paying in ETH.
Most of the campaigns are paying in bitcoin and for the bounties they are paying with their tokens which you can trade for ETH.
Most of the campaign will not pay in the form of ETH, Even though ICO bounties will be paid in the form of token.
I have never seen any campaign paying in terms of ETH, but they will pay in the form BTC and altcoin of that particular company.
Actually there were some campaigns who paid with the combination of ETH and their tokens but currently there is no active campaigns which is paying in ETH,but if it is bounty means token will be rewarded for your work and participating in the bounties is always risky either you will get huge reward or nothing.