My guild doesn't use any kind of loot system whatsoever. I upgraded to the loot systems package for the sole purpose of using the Items Received, Raid Analysis, and raiding members stat. So I can definitely attest to those features being very nifty, regardless of your loot system. However...
DKPSystem supports EPGP. How this works, and how to get the DKPSystem mod to work with it is something I can't help you with. As I said, we currently don't use any kind of system and I've never had the pleasure of playing with the GRSS mod very much.
So I wholeheartedly recommend upgrading. I'm sure someone else will chime in soon who can help with the EPGP specifics.
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Ieyasu - Organizer,
Ex Cineribus