Well, not exactly. The TEVES ABS can be separated into two systems: the boost circuit which gives you power brables and the ABS circuit which provides the antilock feature.
If the boost cuircuit goes out, the pedal will get hard (but standing on it will still provide some braking from the front brakes only). If the ABS goes out, the brakes will feel normal but will not prevent the brakes from locking.
The experience described sounded more like a pump relay failure which caused a lack of boost. When the pressure dropped low enough (under 1500 psi AFAIR), the ABS also turned off because it would be unreliable. At this age the relay often needs replacement and is a good place to start since a remanufactured TEVES is $600 from Prior and a relay is about $12.
BTW a good system should provide 10 or more assisted stops even after the red light comes on. If it gets hard with one or two applications it probably needs a new accumulator (about $100 from GMPartsDirect) which is typical at this age.
The car I have the TEVES on (not the Bonneville) has two brake warning lights, a red (boost) one and a yellow (ABS) one. If the red light is on, the yellow will be also. A failure in the ABS circuit (extractable through the ALDL) will not turn the red light on by itself.
There are a series of tests
on the Reatta site for the TEVES that may be helpful.