Yes. ^^
First of all, make sure the header is pinned in ribbon-cable order. Typically, you'll assign differential pairs to adjacent pins, and place grounds on either side (as shielding).
This looks fine when the header pins are adjacent (side by side), but every other pair will be diagonally adjacent. It's not wrong, just make sure you have the correct diagonal and all that.
By "ground", any well-bypassed supply will do. "Ground" is an RF point of view here, and all supplies are equivalent, if they are bypassed together. Normally you'll alternate supply and ground, or group sets of them together.
Unbalanced signals should be placed the same way, i.e., with grounds inbetween. This gives a characteristic impedance of about 100 ohms. (Diff pairs are about 120 ohms. The ribbon cable datasheet will give exact figures for configurations.) An array of unbalanced signals will occupy one column of the header, and the other will be all "grounds".
This is why old school data cables used so many pins, and often a bus driver IC at the transmitter end and a terminator resistor pack at the receiver end. Classic example: ST-506 hard drive bus. Somewhat more recently: parallel ATA was originally 40 pins, but 80-pin cables with special 40-pin connectors, using shorting links to ground every other wire, were introduced when high speed modes were introduced.
Tim