I tried looking for answer, but I couldn't really form my question... So for example, I want to have a folder synced to the cloud in my Dropbox/Copy/Google Drive/OneDrive account, and right now if I want to to that, I have to copy the entire folder in the program's sync folder. Is it possible to just reference the folder in another location of your computer and sync it, without having to copy it?
Short answer, no. You have to put files within their respective brand name folders to perform the sync.
If you have DropBox, and you want to sync OneDrive files, you have to put the OneDrive folder underneath DropBox. Vice versa if you want to sync DropBox files within OneDrive.
Google Drive does not appear as a regular folder in Windows Explorer, so there is no way to perform manipulations like symlinks or junctions on it. Even if you could, the application itself may not support file redirections.
OneDrive does not support junctions.
Yes, it is possible.
If you're using Dropbox you can try Boxifier (http://www.boxifier.com). I'm the author of Boxifier.
It can sync folders to Dropbox without having to copy them to your local Dropbox folder. Just right click the folder that you want to sync and that's all. It has a really nice Explorer integration so you can see which files are done syncing and which are in progress.