it is a bit slippier running front to back, however I think the difference really dont matter. I'd leave it. But, when you think about it, considering the front->back direction as the y direction on a coordinate plane, when you are running diamonds front to back, considering the total area of the absolute vertical vector lengths of the 'y' directional vectors, the y vector sections of the diamond 'cuts' are greater in total area then when you run it side to side. (trigonometry and just plain looking at it)
With that in mind, think, what is slippier for a walkway, vertical slats, or horizontal slats? The answer is horizontal, and with the diamonds running front to back, it is more like a walkway with vertical slats rather then horizontal.
Heres the best example I could find:
http://www.maion.com/photography/_photos/finl2681.jpg
consider that the diamonds running right to left. If the boards were running done the length of the dock, which do you think you would get better traction on when running down the dock and coming to an abrupt halt?
I dont think it will matter too much however considering the size of the 'slats',
I wouldnt worry about it. Still plenty of surface area to grab.