Hello There.
When an emulator does not appear on the Emulator Selection list, you can manually add it to your Emulator Setup. What you can do is to go to your Emulator Setup, open the 'Select Emulator' list and choose an empty slot. Then, begin filling in the parameters as needed. I think the easiest way to do it is to find an emulator that is already set up and use it as a point of reference. Of course, your paths will not be exactly the same and not all options will be used (depending on what features you are using), but that is the basics of it.
However, in your case, I notice from your GameEx.ini that you chose Retroarch with the Redream core for your Dreamcast emulation (Emulator #7). If you go to your Emulator Setup and view Emulator 7, you will notice the command line is the following: Command: retroarch.exe -L ".\cores\redream_libretro.dll" "[ROMPATH]\[ROMFILE]" -f
So, if you do want to have a stand alone setup of Redream, Emulator #7 would be a good one to reference.
I should mention that I have not used either Retroarch or Redream (I use nullDC for my Dreamcast setup), but I believe Redream is only used for Dreamcast.
It may help to know the reason you would like to add a seperate install of Redream. There is nothing wrong with having a separate setup by the way.