Can i populate the empty sites/default/files/ with files from a local installation?
If your two Drupal installs are exactly the same, it is possible. Your biggest problem will be figuring out the name of the files, since they will have some hash value generated by Drupal. I don't know exactly how this is generated, but yes it is possible.

Now while this is possible, it's not a long term solution. If you had a live site, and something was failing to generate the aggregated css and js files, it could be a quick short term solution until the real problem was found and fixed.

I believe that you have asked about this already and received answers about file permissions etc, some of this which doesn't belong here, since it's about setting up a server and not Drupal itself. I would advise against pursuing this path, and instead try to resolve the real issue. If you want to upload files, use image cache and a lot of other modules and features you need to resolve this anyways. Making a hacky unstable solution will do you no good.