From what I understand, ps2 emulators can't really run ps1 games, so that's the reason for that. Not to mention that most emulators are made so people can casually play a game rather than it accurate to the hardware itself. So if a ps2 emulator would work, more than likely it'd load faster than official hardware.

As for emulators we use, at the moment I am using ePSXe 2.0.5. I'm certain that's what other people are using, but that's what I am. I hope this helps :)