Hello Reinhard,
the short answer to your question could be a simple "it depends". In some cases calling DLL functions can be easier than in other cases and it mostly depends on the language the dll was built on.
During my activity I have succesfully used DLLs for vendors like Hilscher, Moxa, Brad-Molex, Kvaser, Peak and others and I can admit that in some cases it was a challenge.
You may start reading the following resources on the argument:
FAQ: Using Dynamic Link Libraries with NI LabWindows™/CVI™
Linking to Functions Defined in a DLL From LabWindows™/CVI
Calling a DLL in CVI: Explicit Linking vs. Implicit Linking (Dynamic vs. Static)
Take a look also to this example:
Using DLLs built with Visual C++ in LabWindows/CVI
