Well ... know my friend uses many of those in his architectural visualisations (uni. student) ... and the site claims :
"3. Archive3D.net is not responsible for the further use of this 3D model and does not consider the usage claims due to lack of tools and authority to control, confirm or guarantee the accuracy of personal data and law information.
4. This model may be freely modificated or elaborated."
So if no one uploads someone elses model that is under some legal restriction, there should not be any problem. (and even if someone ripped it off from someone - you should be ok, as you didnt know it - it would be the uploaders responsability)