You are correct in thinking that the vehicle's wheel speed sensors are used
by both the ABS and the ETC systems.

What would be good is to have the machine scanned for possible ABS trouble
codes lurking.  That would probably narrow the search for what ails the
system in short order.  One thing you might try in lieu of having it scanned
is to inspect the connectors and wiring to each wheel's speed sensor.
Perhaps clean each connector to get rid of any grunge, then unplug it and
plug it back in a couple of times.  Also check for damage of each sensor's
special flexible wiring harness while you're in the vicinity of the sensors.
Several posters on these groups have offered similar advice to others with
your symptoms.

I hesitate to say with certainty that your speedometer problem is not
associated with the ABS/ETS problem.  If there is a link it would almost
have to be a weird mechanical thing it seems to me.  Your machine's vehicle
speed sensor is entirely separate from the wheel speed sensors.  Its output
goes to the body control module and from there to the instrument cluster via
the class 2 serial data link.  If the ABS/ETC malfunctioned and caused some
kind of mechanical oscillation of the "drive shaft" then maybe the VSS could
put forth a bogus signal that would register on the speedometer.  No way I'm
hanging my hat on that happening though.  Just trying to make some sense of
the speedometer behavior and coming up short.

You