Flyin Miata also uses a BOV in their MSM intake kit, but they seem to imply that there is something different about the BOV they sell that makes it OK with a MAF:
The piston is actually fitted with a piston ring for a perfect seal. Combined with a well-chosen spring, this means the valve can be used on a car that uses a MAF or AFM to measure airflow. We'll say that again - it will work with a stock ECU.