Yes, it is possible, but there's only one way that I know of since they removed the colours advanced settings dialog (possibly third party utils to do it too).
Press +R and type
regedit (or look for it in Apps).
There you need to edit
IconVerticalSpacing, the former is for the horizontal spacing and the latter for the vertical one (they range -480 to -2730).
For the horizontal space, the closer to -2730, the more space between icons and vice versa (but here you're changing the size of the box surrounding the icon:
The same for vertical space, but you're changing the separation between the boxes that surround icons; for example at -480 they overlap:
To apply the changes the only way I know is logging off and back on again and then moving one icon, restarting Explorer doesn't cut it this time.
If you have access to a Windows 7 machine I'd say it's easier to change there the spacing using the regular options in the advanced settings dialog for colours, and then looking at the registry for the values you'd like to translate to your Windows 8 machine.
In any case these would be some of the values to help you edit those values:
By the way, another useful value to change there is
BorderWidth that controls the width of the borders of windows.