VPN service wants access to keychain. Safe?

Typically, when an app is given permission to access the Mac's Keychain, it is to retrieve the password that is used by that app. Is it possible that this app can be malicious and attempt to access all of your Keychain passwords? Sure, but that would be true for any app that uses the Keychain. NordVPN is one of the more "trusted" VPN providers out there and I would suspect that they are not using their VPN apps for this purpose, but it always pays to be vigilant.

The only way to know for sure is to perform a data capture before, during, and after you run the VPN app to see what it is "up to." However, in this case, I don't believe this is necessary.

FWIW, I do use VPNs. I only use them for two specific situations: 1) To access my home network from a remote location. In this case, I have networking hardware that supports VPNs. I then have a VPN client on my portable Macs and iOS devices, that allow me to create a secure tunnel between them, and 2) When I use any of my portable devices that I connect to an unsecured wireless network, like at an airport or coffee shop. In this case I went with PIA as my VPN provider. Regardless, I don't rely on using this VPN for banking or other critical communication unless absolutely necessary. I basically use it to prevent others nearby from attempting to gain access my device or its communications. I totally agree with the others who have replied to you that using a VPN is no way a 100% fool-proof security method, but I do believe it has a valid purpose for certain situations.