The Serviceability Agent supports x64, and jstack etc work fine.
clhsdbproc64.sh however fails to produce stacktraces:

(5.10)$ ./clhsdbproc64.sh 16904
java version "1.5.0_24"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_24-b02)
Java HotSpot(TM) 64-Bit Server VM (build 1.5.0_24-b02, mixed mode)

Attaching to process 16904, please wait...

hsdb> where -a
Exception in thread "main" java.lang.ExceptionInInitializerError
        at sun.jvm.hotspot.CommandProcessor$27.doit(CommandProcessor.java:920)
        at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1243)
        at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1213)
        at sun.jvm.hotspot.CommandProcessor.run(CommandProcessor.java:1116)
        at sun.jvm.hotspot.CLHSDB.run(CLHSDB.java:74)
        at sun.jvm.hotspot.CLHSDB.main(CLHSDB.java:18)
Caused by: java.lang.RuntimeException: cpu 'amd64' is not yet supported!
        at sun.jvm.hotspot.ui.classbrowser.HTMLGenerator.initialize(HTMLGenerator.java:185)
        at sun.jvm.hotspot.ui.classbrowser.HTMLGenerator.access$000(HTMLGenerator.java:27)
        at sun.jvm.hotspot.ui.classbrowser.HTMLGenerator$1.update(HTMLGenerator.java:171)
        at sun.jvm.hotspot.runtime.VM.registerVMInitializedObserver(VM.java:306)
        at sun.jvm.hotspot.ui.classbrowser.HTMLGenerator.<clinit>(HTMLGenerator.java:169)
        ... 6 more



This is true for tests on JDK1.5.0 and jdk7.