Hi,
Technically, you can use a CIN or DLL in your LabVIEW Real-Time program. However, the RTOS on the real-time processor does not support the entire Windows API (although the most commonly used functions are included). In most cases, if your DLL or CIN works on a Windows machine it will work on the RTOS, but if your C code is making function calls that are not included in the Win32 subset that the RTOS has, then the code will fail.
Regards,
David D. - Application Engineer - NI France