I would've bet money that Thomas would be among the dissenters, but Rehnquist? Did not some of his decisions in the early days of the Drug War reduce the 4th Amendment to ashes? Perhaps he's repenting now that he sees his days are numbered . . .
Considering he has cancer himself.... I think he would have recused himself, if he had actually used medical marijuana, but I'd place a small bet -- maybe doubling up on the one I would've won earlier -- that he has first-hand knowledge of some people who do.