You won't need an exit permit hiking from a trailhead from the West side. I've done a couple of trips from Road's End in King's Canyon NP via Forester pass, another of the same via Colby pass
Some slight clarification. It depends on the definition of west side. If you approach Whitney Summit from the west on the JMT but having accessed the JMT from the east side in Inyo ( like Onion Valley or Horseshoe Meadows) you will need a Trailcrest exit permit to descend on the east side to Whitney Portal . I did. Other option is tag the summit and head back on the west side to any of those start points and no Trailcrest exit permit needed, as stated.
