According to https://www.vmware.com/support/converter/doc/conv_sa_552_rel_notes.html#interop it does not support 6.0
A couple of routes - set up a an NFS server on your network and connect the old ESXi host to it and copy the VMs to NFS data stores and then connect it to your ESXi 6 host and move the VMs to what ever data store you want