If it is Oracle 5, which is essentially a clone of RHEL 5, you can also use VMware Converter installed on a tertiary Windows machine, just choose source "VMware Workstation or other VMware virtual machine" and point it to a local copy of your VM. Be sure to record the mac address that was used in fusion because you may need to manually apply that mac to the VM in vSphere. For reference, Fusion uses the E1000 NIC so at the destination if you would like to switch to vmxnet after reinstalling vmware tools, update the mac in /etc/sysconfig/network-scripts/ifcfg-eth0 or ifcfg-em1 whatever you are using.
Oracle 6 cannot be converted and would have to be exported as described, and then apply the new mac after tools install.