This is another one of these retarded things that parts companies come up with, along with "canbus" compatible light bulbs.
All B5's have OBD (on board diagnostics). This has absolutely NOTHING to do with the catalytic converters.
What the ******* are actaully getting at, is that later cars have two lambda sensors one before and one after the cat, allowing the car to perform diagnostics as to the health of the cat.
Your car will have one lambda sensor. This means you probably want a "non-obd" cat.