I can't get either reicast-libretro or the standalone to compile for RPi, so you're out of luck.
I don't know, must be something weird with your HDMI handshake. Perhaps try using a preloaded EDID (don't know if that's even possible on the Pi).
Hi again escalade,
Don't know if you want to look further on this subject but I check on retropie, it seems they've done a fork of reicast here :
GitHub - RetroPie/reicast-emulator: Reicast is a multiplatform Sega Dreamcast emulator
perhaps it will allow to compile...