I figured out how to do this and thought I'd post my solution here in case others find it necessary to do this-
In companion, set up the connection to OBS like you usually would, and then create a regular button.
The press action is obs: Custom Command
For Request Type, enter: CallVendorRequest
For Request Data, enter: {"vendorName":"downstream-keyer","requestType":"dsk_select_scene", "requestData": {"dsk_name":"DSK 1","scene":"Overlay 1"}}
Above, replace "DSK 1" with whatever you called your DSK tab, and then replace "Overlay 1" with whatever your scene name is that you want to activate.
If you want to hide whatever is displayed, instead of "scene":"whatever", use "scene":""