They're working on it.

They've got experimental 64-bit and ARM support in the repo, but they're still ironing out some false-positives. [1][2]

[1] - https://github.com/DynamoRIO/drmemory/issues/1839

[2] - https://github.com/DynamoRIO/drmemory/commit/dcb3af0836e0d75...