Given my issues with even PS1 emulation on PS3, I doubt that they've designed an emulator that will run PS2 games without any additional hardware. So basically, these will be ports, requiring some additional coding to make each game playable.
If you have issues with PS1 emulation on PS3, that just speaks to the emulation not being perfect. The article talks about how there's some PS2 games that "just don't work" which likely means that this is emulation with a variety of speed hacks to get everything full speed, without an emphasis on accuracy.
Also roughly a year ago there were several articles out there saying that Sony had started work on a PS2 emulator for PS3. At the time, people thought maybe they were trying to get PS2 BC back. Now we know they were actually just doing it to sell you the games again!