No reason it should not work.

Some LEDS with internal electronics can be dimmed by reducing the supply voltage. Other LEDs which are generally listed as non dimmable will operate at a relatively constant illumination level as the supply voltage drops and then all of a sudden go out (once the voltage drops below the diodes forward voltage). PWM modulates the LED output by switching the LED off and on at full voltage (which is at or above the diodes forward voltage); but, varying the on time to adjust the illumination level. As such, even a non dimmable LED should light up and dim successfully with a PWM dimmer.

Something to be aware of with LEDs. Some have internal circuitry that allows the LED to be inserted in the socket without regard to + or -. Others require that they be wired up / inserted in the socket with the appropriate terminals connected to the + an - supply.

Planning to bench test the completed set up in the instrument cluster is a good plan. There can always be some hidden factor that crops up and you want those sorted out before the cluster is back in the car. You may also find that even with dimming, some high power LEDs may still be too bright when the dimmer is on minimum. Not all dimmers can dim to zero pulse width.