What do you mean by proftpd account?? You mean a normal user account that you will use via FTP to update web pages?? If so, you can create a normal user account and change its home directory to "/var/www/html" in "/etc/passwd" or better yet, create a syslink folder in that proftpd user account to /var/www/html. For example, you have /var/www/html and your user account name is agar. Inside /home/agar, you want to create syslink "web" that when you browse it, it will go to /var/www/html. So you would do,
When you log in via FTP, SSH or whatever, browse to ~/web folder and you will be there at /var/www/html in no time.
ln -s /var/www/html web.dir.name