Where are you finding that reservation metric with the management pack? In 6.6.1 I didn't see that available on the reservation object.
In 6.7 I can find it when looking at All Objects > vRealize Automation Adapter > Reservation > [said reservation] > All metrics > Memory, etc.
I tried 6.6.1 but it broke more than it fixed in my environment. I didnt really explore it much more than that after being unable to get business group specific virtual machines to show up in their respective custom group/dashboard. They removed a useful Inventory Tree "Automation Tenant Business Group and Virtual Machines" that my custom groups relied on but i found a work around with 6.7. I even downgraded the included vRA adapter in 6.6.1 by reinstalling the v2.1 MP from VMWare's website and gained back that useful tree. No clue why they dont offer other versions through their solutions exchange.
6.7's vRA MP also brings back a number of new inventory trees, now known as "other inventories" in 6.6.1 and 6.7, and also re-establishes relationships between business groups and VMs that were removed in 6.6.1, so my custom groups work again.