Its possible to hitch, you just have to be patient, which is hard because it can be bloody hot. There are people going but, but its not yosemite. If you run out of patience there are folks in Bishop that ferry hikers for $20-30. The sporting good store in town has a list of the current people.
I have taken the CREST bus from Mammoth to Bishop. I assume that the other direction is similar. I didn't have any problems with it. It arrives on time, you give the driver the fare and an hour later give or take and you are there.