Yes, our Arduino VNH5019 library is written for the Arduino IDE, so it has no features that help people use MATLAB. However, you could still use it in a system that sends commands to an Arduino from MATLAB. (We do not have any examples for doing that.)
By the way, if you just want to control your motors over a USB interface, you might consider using four of our Simple Motor Controllers. You could write MATLAB code to send serial commands to the Simple Motor Controller's virtual serial port over USB.