It seems unlikely that it would help much. From what I understand, PS3 emulation is CPU-limited more than anything. It shouldn't take all that much graphics hardware to render 10+ year old games that were originally designed to run on a graphics chip mostly equivalent to a (circa 2005) Nvidia 7800 GTX, even at much higher render resolutions. The real performance limitations come from trying to emulate the PS3's 8-core IBM Cell processor on other CPUs, and upscaling isn't going to help with that.
And FSR upscaling was already added to the leading open-source PS3 emulator well over 2 years ago. At the time, the developers stated that they would not be supporting DLSS, because it required access to motion vectors, something their emulator (and perhaps PS3 games in general) didn't use. The main advantage of FSR2+ is that it is also able to utilize motion vectors for better results, but much like DLSS, if the emulator doesn't have access to that, it likely won't be implemented. FSR3 Frame Generation also utilizes motion vectors. It's technically possible to implement frame generation without access to that, but the results likely won't be particularly good.
Even if it were possible to implement frame generation in a PS3 emulator, that feature is usually best reserved for games that already run well, to make them look a bit smoother on high refresh (120+ Hz) displays, rather than something to fix performance issues with games running at low framerates. Since the games are still effectively running at or below their frame rate with the feature disabled, but then have to wait until a subsequent frame is rendered before generating an interim one between the two, it effectively increases input latency rather than reducing it. So while a game's motion might look smoother to an observer, it won't really feel smoother while gaming, in terms of responsiveness. The generated frames also tend to look notably worse then the rendered ones, and while that might not affect visual quality so much at high frame rates, at low frame rates the artifacts can become more noticeable. So if an emulated game has unplayable performance now, frame generation isn't likely to help with that.