In Fusion 4.0.1, as in the June 2011 Beta, there is no VMDKMounter anymore, despite MacFUSE having been updated to OSXFUSE:
... which indeed works in 64 bit mode and with Lion.
In the meantime, one can always install Fusion 3.1.3's VMDKMounter with Pacifist (the installer metapackage is located inside the Fusion installer application): that should work, hopefully...