How can i add and run a labview executable file inside the vi and grab the output of the executable file to be used in the vi?
to run an executable you use SystemExec function.
To get the output of your (LabVIEW-made) executable you need to program some data transfer means: you may use network functions or file functions. In both cases your "LabVIEW executable" needs to provide that options…
I really hope they lack the source code. Otherwise, this question show an awkward architecture. If you have the source code, you're complicating things by making it an exe. If you don't, you'll need to redesign the exe's functionality to extract information from it unless it's already setup with something like a shared variable to store the information.