Is it possible to use multiple keyboards?

Yes, you can use two keyboards for two players, provided that each player's key mappings don't overlap with each other, otherwise there would be problems.

The same can be said for other local multiplayer games, co-op or not.

Games (typically) will only see a single keyboard, as presented by the system. Therefore, you cannot use multiple keyboards with the same bindings.

In most (but not all) cases, keyboard events are handled and mixed by the operating system, not by the game. Unless the game has direct hardware read support (some do), the OS supports it, and are built to support this multi-keyboard infrastructure, the game will only ever see the single "keyboard."