if you add .lst into the es_system.cfg under dreamcast (located in etc\emulationstation) then run
/etc/init.d/S31emulationstation restart this will stop the changes being overwriiten. Dreamcast core needs to be LRReicast and naomi_boot.bin needs to be in the bios folder, copt .lst/dat or .lst/bin into dreamcst and reboot. Naomi and Atomiswave games will run from the dreamcast menu. Would be better for next release of Batocera to have a seperate fold for Naomi and Atomiwave roms to be added out of the box. This only works with roms that are in .dat or .bin with the right .lst config file correctly calling the .bin/.dat filename, it dosn't support mame naomi/atomiswave roms at the moment.
an example is dolphine blue.dat and dolphine blue.lst (both are needed) to work as its linked in Batocera throught the .lst file. An .lst file is a text file using the folling syntax:-
"Dolphin Blue.dat", 0x0000000, 0x08000000
the .lst file would be 1KB in size and the .dat file about 131MB in size, each .dat file with very in size deponding on the game.