Short answer yes. You don't have have a gpu some you don't need to worry about it.
I think it really depends on the power brick. Check the 12V Amp rating on brick and see if exceeds the spinup peak amperage of the hdd.
eg. the WD WD40EFRX uses 1.75Amp at peak which is 5.25amp for 3 hdd.
If you're using a 160Watt 12V brick, it should have 13A