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.
To what extent does its easy C interop make up for this?