Dropbox Backup - 2 Questions

Megan, a question about this statement in the Dropbox instructions: If any of the folders are already backed up to another cloud storage provider (like iCloud, OneDrive, or Google Backup and Sync), disable those backups and ensure your files are back in their original folders on your computer. (If you’re not sure how, consult that company’s help center).

Will Dropbox automatically not back up a folder that is already being backed up by iCloud? In other words, if I fail to disable an iCloud backup for a folder I've chosen for my Dropbox backup, will Backup automatically leave that off the backup without causing any issues? I ask because there are a few folders in my finder which I am not sure are backed up by iCloud. One example is the Music folder. In iCloud drive there is a "Music" checkbox, which I have checked, so presumably it is backing up everything that is in the "Music" folder in Finder, but I don't actually know. There is also a Pictures folder, in which I have some pictures that I don't think were ever put into the Photo app. and therefore, I don't think are being backed up by iCloud, as I think that only backs up the official Photos app. 

Thanks,

Mike