You can have a static route to any local device, this is essentially what subnet membership does.

For example, if I have IP 192.168.0.2/24 assigned to eth0, my routing table will have:

  192.168.0.2/24 dev eth0 proto static scope link

I'm free to add a local route to a device outside 192.168.0.2/24 though:

  192.168.10.1 dev eth0 proto static scope link

This just indicates that I should be able to resolve the MAC address associated with 192.168.10.1 through an ARP query, same as other devices on my subnet.