Regarding the line appearing in Kingdom Hearts: Birth By Sleep while running in PPSSPP using Direct3D9 backend, according to test on real PSP that line is NOT supposed to appear. This turns out to be a Direct3D9 issue actually, so it has nothing to do with OpenGL dual source alpha blending extensions. It also appears to only affect Intel HD Graphics 2000. I tested for this issue a desktop with Intel Core i3-3220 Intel HD Graphics 2500 driver 15.33.30.3958 and a laptop Dell Vostro 2521-9566 Intel Core i3-2375M Intel HD Graphics 3000 driver 15.28.22.64.3517 and COULDN'T reproduce in both cases.
PPSSPP issue thread for this: https://github.com/hrydgard/ppsspp/issues/7040
Regarding rpcs3 it doesn't work because it requires at least OpenGL 3.3. Intel HD Graphics 2000 which is bundled with 2nd generation Intel Core processors is capped at OpenGL 3.1. You need at least 3rd Generation Intel Core processor with Intel HD Graphics 2500/4000 to hope for it to work.
See: https://github.com/DHrpcs3/rpcs3/wiki/FAQ#what-are-the-hardware-requirements-i-need-to-run-it