The Pokemon data structure, you mean? Yes it would, though you'd be rewriting the Storage System to accommodate the shorter data structure. However, unless you're okay with losing things in that structure it's not going to be a lot of space saved. You can shave off like 12 bytes of space without losing anything important (except Pokerus, but who is realistically going to run into that in your hack?) But that only gives you like 74 more Pokemon slots in the existing space. Your restructure will depend on what you plan on using for your hack. For example, if you don't care about contests or ribbons, you can cut those out of the data structure and get like 10 extra free bytes. If you're getting rid of trading, you can get rid of OT OTID and OTSID fields. It's really up to what the hacker wants.
I don't know enough about how SRAM is laid out to say for sure if restructuring SRAM would be useful to increase Pokemon storage space. I know that there are regions in the save that are not used in English files (eReader stuff, for example). In R/S I know where that area starts but don't know where it ends. If it's the whole rest of that block from where the data starts until the start of Pokemon Box data, that'd be enough space for 23 Pokemon without compression. Perhaps cannibalizing the backup save for more Pokemon Storage could be a solution, but the backup has saved me from losing my file a couple of times in my youth, so that's a big loss in my opinion.
The issue is that the things you'd be able to prune from the space that isn't already used to store Pokemon are so small that I doubt it would be worth it to completely restructure SRAM to reclaim. The Pokemon themselves are huge compared to much of the other data in SRAM. Wiping out whole features that get saved would probably be a better bet. For example, getting rid of Secret Bases entirely in Ruby and Sapphire and using that SRAM space for Pokemon gives you 40 extra slots without compressing the Pokemon data structure. Block 3 in R/S saves Television Shows and Contest winner portraits. Getting rid of that gets you 49 extra slots. Getting rid of the eReader, Secret Bases, TV shows, and Contest Winner Portraits only nets us 112 extra Pokemon in the save, for a total of 532. It's something but with Pokemon totals as they are nowadays it's a drop in the bucket at the expense of nuking features that you seem to have interest in porting into one, mega Gen 3 game.
For reference, pruning the data structure down to 67-bytes (which is as far as I'd be comfortable) and using the space we just freed up in addition to the currently existing space gives us enough room for 635 Pokemon. Getting rid of all contest data as well puts you at 57-bytes per Pokemon which under the same conditions gets you 746 Pokemon. I'm personally not willing to get rid of Secret Bases, though I might be okay with losing TV shows and rewriting what data gets saved for Contest winner portraits to shrink it (each portrait is 32 bytes each and there are 13 of them).
