Hi,
When you are powering the system from the NEO USB, the 3.3V regulator on the NEO breakout is “back feeding” power to the 3.3V rail on the OpenLog Artemis (OLA). That’s OK.
If you also have LiPo connected, the OLA’s 3.3V regulator will also be powered up. One regulator output will be slightly higher than the other and will “win” in terms of delivering power to the combined system. I’ve never seen this cause problems or issues.
You may find that your LiPo battery still discharges when you have the NEO USB connected. But that should be the only weird thing that happens.
I hope this helps,
Paul