In LabVIEW, the source code is the diagram. It gets compiled into machine code, of course, but the diagram really is the code. It is not converted to C and then to machine code.
LabWindows is C code. C code is not a diagram. However, there are tools for using LabWindows front panels in LabVIEW. If you have already built something in LabWindows, you can convert the front panel to LabVIEW and call the code through a Call Library Node. (In fact, I build all of my sparse enums this way
.)
Another thing you can do is to compile the code of either language into a DLL and call that DLL from either language.
I hope that this helps,
Bob