Yes, the GDDR5 or infact any GDDR does not effect the DDR present on the rig. They are not related.
GDDR is the RAM on the Graphics Card and the DDR is what you put on the mobo.
So you are absolutely good to go with that card in that rig.
Your PCIe X 16 slot can handle that GPU. The Light blue one on the board.
Although the card may not need external power the card is still going to be pulling power from the PCIe slot.
Make sure you have a 400-500W PSU.