If you don't check "Preserve Vector Data" in the assets catalog, XCode will generate 3 PNG files from the PNG. So, not much difference in terms of build size. I would prefer PNG, because, otherwise, creation of PNGs will take time on the designer's side. Automatic job is cheaper then human job. Also, it's easier to track changes in vector. It could even be staged by Git. Easier to maintain, when it comes to updating images.

Second - this forum contains only the opinions of developers and you can never get certainty that your app will be approved. By the way I noticed some users have apple sign near their nickname. I suppose they are developers hired by Apple and acting here as official support. May be I'm not right.