I've got a CentOS server and I wish to determine if you'll be able to share with the ftp user permissions "over" the Apache user? If I produce a folder with Apache (with 755 privileges), I can not take it out of ftp.

Just add FTP user towards the same group as the Apache user. For instance, in case your Apache user within the apache group (default in CentOS) run:
sudo useradd -G apache ftp_username