is the clock signal measurable?

Yes it is possible.

You should have your scope on a 1meg input, 50 ohm will shut down the
oscillator.  You should be able to measure a 4MHz signal at the OSC2
pin.  

You should use a parallel cut crystal NOT a series cut.

Is it possible that the oscillator configuration bits could be programmed
incorrectly?

You really can't.  It is something you specify when you order.
If you can pull some kind of part number off the crystal and check that
with the manufacturer, you might have a chance.