FYI, another car to google is the Lancia Delta S4 Rallye (Group B).

It used a roots-style positive displacement supercharger and a conventional exhaust driven turbocharger and competed in the FIA Group B Rallye Championship in the 1986 season.

From idle to 3500rpm or so, the clutch-equipped supercharger pulley was engaged, allowing the blower to hork in about 12 psi of boost by 3000rpm.
By that point, there was enough exhaust volume produced by the relatively small motor (I think it was 1.9 liters) to drive a much larger turbocharger.

By 4000 rpm, the following changes took place:
a) the supercharger pulley clutch disengages, allowing the pulley to free-wheel on the input shaft.
b) a diverter valve opens, allowing the intake charge to bypass the supercharger altogether.

So yes, the system would physically work, but modern turbocharger design makes the concept of twin-charging obsolete and unnecessarily complex.