I've got Autometer Cobalt gauges (LED) wired into the dimmer switch of my wife's truck, and yes, they dim some but not like the dash/gauge cluster lights. They dim at a different rate IIRC but idk much about resistors & that sorta stuff to remember why. My SPA gauge (also LED) is wired to the dimmer & no bueno.
Cornell, when you did the LED lights in the dash & cluster, did you have to wire in resistors or use special resistors for the voltages coming to the factory bulbs? I've read that procedure but it's be so long I can't remember how to do it. But if resistors or resisted LED were used, then maybe that's why yours dim properly with the factory dimmer?