I often like using simple editing software on my iPad, however if I were to shoot in RAW and then export a photo as a png/jpeg and then saving it on snapseed, would using the program make the resolution worse?
So, the short answer if you're editing and saving from Snapseed is yes. There are a couple of reasons why this will result in reduction of quality:
You've discarded data from RAW to PNG/JPG in the first place. This now gives less information for Snapseed to work with and so further edits could result in even less data, especially in the shadows and highlights for subsequent saves.
JPG is already a lossy format and subsequent saves result in even more loss from the original compression. Ideally, to maximize JPG quality, you want to always start from the RAW data. Now PNG isn't inherently lossy, but see point 1 and then your choice of subsequent output formats from Snapseed will matter as, if I recall correctly, it converts to compressed JPG on output.
In any event, for web display and usage, I'd be surprised if any would really be able to tell. If you're looking to print large (e.g. greater than 8x10) then I would avoid this workflow altogether, but for small usage, I suspect you would struggle to see the effects unless your JPEG compression was really strong.
The answer is definitely YES but if this iPhone use only then it probably doesn't really matter as the destruction of your image is part of the aesthetic of SNAPSEED.
NIK Filters make a sharpening plugin and a Analogue FX plugin for photoshop that you can use with 16bit images - as NIK make SNAPSEED then that's the direction you could go