Is Truecrypt/Macfuse supported on Snow Leopard with 64-bit kernel?

As of MacFuse 2.0, the entire stack is available in 64-bit. Not sure about TrueCrypt, but you don't seem to be getting that far anyhow, probably because the default MacFuse build is broken. You can download a hopefully fixed 64-bit MacFuse at http://static.caureadotorg/MacFUSE/MacFUSE-2.1.7.dmg

No, it is not. The kext needs to be re-written to work and as of yet no one has done it. Here's an explanation from the original developer for MacFuse Some Answers - Amit Singh