Doesn't the Caddy dizzy also have a reluctor for the ignition as well?
Yes. The Vortec piece is not a distributor in the traditional sense. There is no crank sensor built in so there's no way to trigger spark. I don't trust it for reliability, either. I've seen plenty of oil leaks, cracked cap retaining ears, and rotor attaching pads that are loose on the shaft to decide the plastic part just isn't worth using. I have a pile of 'em here at the house that were removed from buses in our fleet.

Early V6 Buicks with SFI used a cam sensor in the distributor. Certain S10 trucks with 2.5L engines also had a hall effect sensor added to the distributor which could be used as a cam sensor.