The latest release of valgrind (1.13.0, released June 15) claims support for os x 10.12. I built the current release of rapidjson and ran the tests. Indeed, the tests now run (with previous valgrind versions, they died). However, a number of valgrind unit tests failed. I'm not experienced in interpreting valgrind output, but it looks like most of the failures are os x system libraries. It may be the case that a new suppression file is all that's needed. In any event, I've attached a file containing the verbose output of the valgrind unit tests.
rapidjson_valgrind_test_output.txt