The 8 pin CPU power plug is EPS, ATX was designed for normal PCs, while EPS was designed for high end desktops and servers so it added the 8 pin connector, so yes it will work fine.
It depends on the board and the CPU, many are fine with just having the 4 pin plugged in, some are picky and always want an 8 pin plugged in. Consult your motherboard manual.