Is Kearsarge Pass the standard resupply exit for JMT and Rae Lakes permit trips?

For the southern Sierra, yes. The Charlotte Lake junction on the JMT, around mile 157, is where a side trail leads toward Charlotte Lake and over Kearsarge Pass to the Onion Valley trailhead. That crossing is the standard way JMT thru-hikers pick up a resupply in the final stretch, since it is the last practical road connection before the trail commits to Forester Pass and the Whitney finish.

It serves section hikers just as well. A classic point-to-point runs the JMT from the Woods Creek area through the Rae Lakes basin and over Glen Pass at 11,978 feet, then exits via Kearsarge to Onion Valley, capturing the best of the Rae Lakes Loop terrain with different logistics. If you are planning that basin specifically, note the camping limits: one night per lake at the Rae Lakes, which shapes where your nights land.

Two planning realities follow. First, because Kearsarge is both an entry and an exit for so many itineraries, the trailhead quota is the most contested of the Inyo JMT feeders, so lock in permits early or watch for returned dates. Second, an exit over Kearsarge is not a shortcut in effort terms. You cross a high Sierra pass with a multi-day pack either direction, so budget it as a full hiking day, not an afterthought at the end of the itinerary.