As suggested by eewhite HP support should be able to help you here.
The quick specs list the following relating to HPE Graphics cards
HPE Graphic Options
NOTE: Up to five cards are supported on the DL580 Gen8. Supporting
multiple number of cards on the DL580 Gen8 blocks some active IO cards
as follows due to space constraints:
For 2P config: Max of 2 double-wide cards are supported on slot 6 and
slot 9 (slot 8 is blocked)
For 3P config: Max of 3 double-wide cards are supported on slot 3,
slot 6 and slot 9 (slot 5 and slot 8 are blocked)
For 4P config: Max of 5 double wide cards are supported on Slot 1,
Slot 3, Slot 2, Slot 6 and Slot 9 (slot 5 and slot 8 are blocked).
NOTE: HPE DL580/DL585/DL980 Power Cable Kit (631660-B21) is required
for Graphics cards. Each cable kit has two 8-pin connectors (one 150W
and other 225W) and can support up to two cards. For three cards, two
cable kits are required. For five cards, three cable kits are
required. The cards pull up to 75W of power from the IO slot and the
rest from the auxiliary power connectors.
NOTE: Both UEFI mode and Legacy Mode are supported.
NVIDIA Quadro K6000 PCI-E Graphics Adapter
730874-B21
NOTE: Supported at Gen2 speeds
NVIDIA Tesla K40C 12GB Computational Accelerator
753960-B21
NOTE: Supported at Gen2 speeds
NVIDIA GRID K2 Reverse Air Flow Dual GPU PCIe Graphics Accelerator
753958-B21
NOTE: Only three cards are supported with MS Windows Server 2012 R2
Auxiliary Power Cables
NOTE: The DL580 Gen8 supports six auxiliary power connectors
HP DL580/DL585/DL980 Power Cable Kit NOTE: Order with GPGPUs for
providing additional power to the IO cards.
631660-B21
@chicks
Sorry I should have provided a link.
For HP quick specs I usually use the Quick Specs offline utility which can be downloaded from this page
http://h71069.www7.hp.com/quickspecs/overview.html
HP PB Application link is near the bottom of page.
It will take a while to update ( depending on network connection and selected product filters) but has reasonable search facility for just about every HP product made.
OAM