The memory utilization graphs in Orion and Virtualization Manager show different values for the same node.
The reason for the difference is that Orion collects data directly from the Virtual Machines, through SNMP, while Virtualization Manager collects data through the VMware API. Orion displays the amount of memory allocated to the running processes on the given guest, but this does not necessarily mean that that amount of memory is actively used. Virtualization Manager and VIM displays the actual, active memory utilization value.
Despite the difference in the data collection method, the data displayed in Orion and the data displayed in Virtualization Manager should not be significantly different.