Assuming such a space station needed to have its central hub not used for docking spacecraft, would it be plausible for a spacecraft to dock on the outer edge of a rotating wheel if the ship approached the station on a tangent to the outer edge, in the direction of rotation? I'm assuming a drone ship, of equal mass, would simultaneously dock on the opposite side of the station to maintain the balance of the mass of the station.
Can you launch an ICBM horizontally?
Sure. Why would you want to? (The Hunt for Red October)
You absolutely can dock on the outer rim. It will be the biggest pain in the tuckus your pilots have ever seen, but yup, it can be done.
There are (at least) two reasons why the central hub is preferred.
You only have to spin the ship on one axis, if you must spin it at all.
You can design the hub so that the docking hub doesn't spin, which is even simpler.
But hitting a docking port on the outer rim means the ship must move on at least two axes. That's what it takes to move in an arc: two axes. This is because you can't actually move up to a point tangent on the outer rim and dock.
Because docking takes some time. Even if you're trying to capture the ship with some cool clamps. The ship is moving in one direction (a straight line) and the outer rim in another (an arc). The "docking time" isn't just a second... it's a minuscule fraction of a second — and if you don't get it right the first time, things (usually the ship) get ripped apart.
So, theoretically, yes, you can dock a ship via the outer rim. It's not recommended.
That would make no sense as it's too complicated and too many things would go wrong.
The station would have a self balancing system which would operate by pumping water to holding tanks around the rim.
As the ship docks, water would be pumped from the area where the ship was to the area opposite the ship.