Whitepaper is a must read if you want to check project and know more about them and their products. How can you contribute if you don't even know what this project is about? The funniest part is that people who don't read go to Telegram and whine that they didn't know about some things/features of project lol 
Definitely yes,I read ICO project's white paper.Because white paper is one important thing to look for when you invest in an ICO project and in order for you to determine whether an ICO project are legit or not.And in the same way you can determine also their bountry campaign if its scam or not.So for me,I do prefer reading the white paper,specially when you want to join bounty campaign.