Putting aside issues with capturing basically vacuum at 8km/s, by doing that you're going to lose impulse that you're going to have to regain, spending more mass in fuel+oxidizer than you gained in gathered gases, unless you use ion propulsion (which ISS doesn't). Also most of what you're going to capture at 400km is going to be atomic oxygen and helium, N2/N share is only a couple percentage points at that altitude.. [0]

[0] https://en.wikipedia.org/wiki/Heterosphere

Clearly you would not choose similar operational parameters and propulsion as the ISS when designing an atmospheric scooper. Not sure why you would assume so, honestly.

There have been proposals to use scoopers with structurally integrated electrodynamic propulsion ("tether without the tether"),[0] which would use zero propellant.

[0] https://forum.nasaspaceflight.com/index.php?topic=44542.msg1...