Thank you for all of the advice, although some of it appears conflicting.
I have examined and traced the wiring from the in-slab 240V metal table saw
outlet back to the panel. Here is what I see:

There are 3 wires going into the saw outlet from the panel end: BLK, WHT and
GRN.
The BLK and WHT are connected to the two hot prongs while the GRN is
connected to the center pin as well as to the metal box.
These wires then go into the concrete slab through a pipe. I can't tell if
it is metal or plastic.
The wires re-emerge about 10' away in a junction box in the wall, From here
they connect with another cable that returns to the breaker panel.
This cable has a RED, BLK, WHT and BARE wire. It is connected to the saw
wire as such:
BLK-BLK, RED-WHT, BARE-GREEN. The WHT wire (from the breaker panel) is
capped off.

What are the new implications of the WHT wire not being employed? Is it safe
in this configuration?

Sounds like it should be re-wired with a 4 wire system as so many have
suggested.

Steve