Yes, that should be a valid configuration. I think there are four memory channels on the R620, so the best population would be {1,2,3,4}{5,6,empty,empty} on each side. You can verify the channel configuration in the manual. The R620 has the flexible memory feature, so there are many memory configurations that will likely work. Thanks
What is the minimum number of 64GB LRDIMM that I can use for my 2 processor r620 for upgrade?   Thanks,  Martin
PoweEdge R620 LRDIMM configuration