DllNotFoundException in Mac Editor; Not Build, Not Windows

I'm trying to use a DLL from a manufacturer that has another dependency DLL. I was able to make this work on Windows by using the @bibbinator method here, by putting both DLLs into the same folder, and adding that folder to the PATH at runtime.

On Mac OSX, however, I get a DllNotFoundException, the same error I was getting on Windows before the bibbinator solution, when Playing the scene from the Editor. Strangely, the error disappears when I build the App.

Any thoughts as to why this might be happening?