I found a resource online I thought I would post here. It is a Wiki with a list of all major game publishers and developers on how they stand with making content of their games. This is only a reference as this is a little outdated, but still some pretty good information. Hope this helps.
http://letsplaylist.wikia.com/wiki/"Let's_Play"-friendly_developers_Wiki
http://letsplaylist.wikia.com/wiki/"Let's_Play"-friendly_developers_Wiki