Is it possible to have 2 different backup systems for different external hard drives?
Yes, Time Machine can do this. All you need to do is connect at least two hard drives to your Mac. One hard drive will be for you to download your raw photos on to manually as you wish. The other hard drive will be your TM hard drive. Because your first HD for your photos is connected to your Mac, it wil also be backed up whenever TM does a backup. Those TM backups will backup what's on your Mac and what's on your photos HD, but you also have the option to select anything you want to exclude from the backup by going into the Options on TM.