It probably doesn't really count, but via OpenStreetMap I found that they have a joint military base that crosses their border.
Everything's airlifted in, but on the photo in this article it looks like they've got at least a couple of ground vehicles there, and presumably tracks crossing the border: https://www.critica.com.pa/sucesos/no-existe-ninguna-base-mi...
More surprising to me is that on the Atlantic coast there's small towns on either side of the border seemingly without a road connection to other adjacent towns in their respective countries, as well as no cross-border connection (but there's a short hiking route): https://www.openstreetmap.org/#map=16/8.6626/-77.3683
So it's not only an issue of crossing the swampland of the greater gap itself, but also the general underdevelopment of these countries.