Even though a line like the one above in the .build.cs file will copy the third party DLL (not the plugin!) to the same directory as your final executable, that copy only occurs during packaging.
Just passing by
I am not sure RuntimeDependencies.Add() is supposed to add the third party DLL of your plugin to the same directory than the final executable (=the final game executable). In my case, with that func, I move the dll from PluginDir\Source\ThirdParty\MyLib\mylib.dll to PluginDir\Binaries\Win64, that is to say a specific Binaries folder inside the plugin folder. My game compiles and runs fine. UE does not crash.
Have you seen the following message:
Also here, in the chapter “Runtime Dependencies”, it seems you have an overloaded Add function (I am not using it):
Peace