Yes, but those signals will be connected to each other. The Flash chip and the SD memory card must release that signal when not used so the other one can use it. I don't know enough of it to say something useful about it.
Flash chip datasheet: "When /CS is high, the device is deselected and the Serial Data Output (DO, or IO0, IO1, IO2, IO3) pins are at high impedance".
That is very nice.
I suppose that the SD memory card does the same.