64-bit SNMP counters for VNX data movers

I'm trying to use a tool like MRTG which essentially uses SNMP to query interface statistics on servers. It uses something similar to snmpget and pulls the ifHCIn/OutOctets statistic and then subtracts the value from the last time that it ran to give you the average speed since the last time it was run. This is working fine on our linux servers and Data Domains boxes but the VNX data movers' counters are reporting values that are too high to be true--in the PB/sec range. So I think there is a problem with the way the data movers are relaying SNMP data for their interfaces and was wondering if I should be targeting a different 64-bit SNMP string.

Currently I'm using .1.3.6.1.2.1.31.1.1.1.6. for ifHCInOctets and .1.3.6.1.2.1.31.1.1.1.10. for ifHCOutOctets

The 32-bit counters appear to be working but they wrap too quickly for my purposes which is why I need the 64-bit ones.

Has anyone successfully used the 64-bit counters? Thanks!