Safe to have USB power and ATX +5 Standby power at same time? (no replies)

I'd like to power my Ramps 1.4/Ardunio Mega from the +5V standby feed (VCC pin on Ramps) from an ATX supply rather than USB. Is there a way to disable the board from drawing power from the USB bus?

Is it safe for USB power and 5V standby to be connected and powered at the same time?