Escrow is good but not a must, you can even miss many good projects if you force escrow on new projects because I've heard few reputable bounty managers complaining that even high quality bounty projects don't want to accept Escrow, the moment they talked about Escrow the team will stop replying and find another bounty manager that don't care about Escrow
It is up to the bounty participants to get this problem solved because if everyone decides they will not take part in campaigns that do not have an escrow involved then the project managers will have to hire one and that is the right way of doing it.
Bounty managers can only help participants if they are ready to bring the respect to the manager by not taking part in bounty-campaigns with no escrow.
Coming back to the topic, yes there can be manipulations in the smart contracts but how will the token do well in the market then after scamming so many participants. I mean they will bombard the social media with negativity and expose them making the project dead.