While we do not have a GUI method to do this, the API provides a list_neighbors function which you can run against a droplet. This will return details on any other droplets you own that are on the same physical hardware. This command can either be used within a program of your own, or via Curl.
You can also use the doctl command line client. Once you know the droplet's ID number you can run this command:
./doctl compute droplet neighbors DROPLET_ID
Thanks for the response. I used the API and it indicated that neither of my servers have neighbors. Does that seem reasonable?
Yup, that means none of your droplets are hosted on the same physical hypervisor, so you're all good! =]