Whether it's legal to log SIC or not, be ready to get grilled on the AC as if you got typed in it if it's a turboprop or tj. I know of people who logged SIC in the BE20 without any school. At the interview, they were grilled extensively on the airplane. After that, they were handed their hat and sent home. They've since quit trying to interview 121 and gone 135. I log all my King Air time dual instead since I have no school, but I'm also still flying part 91.