Just to include my t'pence worth -
I viewed a hospital site on foot recently and there's a bloody great big chimney in the area, when looking, post foot viewing, on goole earth you can see the shadow of the chimney on the ground, go to 3D view and lo and behold the chimney magically disappears, so personally no I would never rely souly on aerial pictures on the internet.
To answer the original question regarding site surveying, when it was not possible for me as an ops bod to visit a site I used to contact local operators and / or pilots I knew in that area, and would request they view the site on my behalf, being the small industry we are I never found this to be a problem in the slightest and it always worked rather well