It helps quite a bit. It's really easy to write a glue layer between Lua and whatever C library you want. The downside is that you still have to actually write that glue.

It should probably be noted that Lua gets along less well with C++, so that glue is a bit harder to write for C++ libs. There are tools that will automatically generate that glue for C++, but I'm not familiar with them.

As Dyson said, it's fairly easy.

LuaJIT2's ffi also makes it a lot quicker.