I decided to do a "manual" scraping (making and/or editing gamelist.xml, uploading own boxart, etc.) because some of the games and/or systems cannot be scraped with either scraper options available. ("No info available" bla bla)
For this process, I connected my Batocera laptop to the same network as my PC and then exited out of Emulation Station via SSH. Using Dreamcast as an example, I made my own gamelist.xml file, placed all of my boxarts in a folder, and then transferred these to the laptop. (It's in /share/roms/dreamcast/)
After everything is complete, I entered Emulation Station, went to option to Update Gamelist, then I checked Dreamcast. All the metadata are there, but the images/boxarts don't appear. I double-checked the image path in both Edit Metadata and in its gamelist.xml, made sure that all the image files are in restarted the system but it's still not there.
I also went to the trouble of transferring the gamelist and the images from a flash drive by accessing the laptop's filesystem and, unfortunately, that didn't help. In fact, it turned out much worse as not every game was "scraped". Again, using Dreamcast as an example, some games don't have images but have metadata, some have it the other way around, and some have nothing at all!
So there. I tried anything and everything but I guess it wasn't enough. Help is always appreciated. Thanks!