Can a ground plane be used as a current return path? (DC only, no signals, no AC)
Can a ground plane be used as a current return path?


The major benefit for using ground planes is that they are used for this very reason. 

For instance, any circuit using a "perfect" ground plane guarantees that the local return path of current is directly beneath the forward (non ground) current flow: -



The bottom-line is that current takes the path of least resistance and, for AC currents, the path of least resistance is the path of least inductance.

In your situation any current that returns through the ground plane, flows close to the forward current path. This minimizes loop inductance, thus minimizes generated interference and received susceptibility to interference.

It's just what happens when you use a ground plane - instantly EMI problems are reduced by a large factor.

As mentioned in the picture, it's an example of proximity effect: -