If they are built right, yes. The problem is you do not get to test the roof with this much weight very often. And any deficiencies (termites, fungis, loose support, rotted wood etc) could cause structural collapse. In the Greater Los Angeles area we can even loose roofs from rain.
Yup. Mine is so steep that it takes proper scaffolding to access it. I'm not worried about snow load. The house is very energy efficient.