[plt-scheme] FFI vs. library implementing RDBMS protocol

I saw the following on Planet Scheme.  It was about Gambit-C, but I  
wondered whether the comment also applied to MzScheme?

> Using the FFI to integrate the C API of your favorite RDBMS is a no- 
> no! If your code is multi-threaded, all your threads will be  
> blocked during a call to the C API. You don't want this. So you'll  
> need a library that implements the native protocol. That's a lot of  
> work, because you'll want it to be robust and efficient.