Hello. I am a beginner, so please be indulgent if my answer lacks pertinence. I have met the same issue lately. I had to discover myself how to resolve it since in here, it seems the simpler and more basic the question, the rarer the answer. I respect that, as it reminds me Spinoza's "narcissism of small differences" concept. (damn, who the heck do I think I am ?!)
Try this as a temporary, yet could work solution:
select your material in the Vray material editor
click on the blue M in the "Diffuse" area
make sure the file you have selected in top is the one that came with your vismat. If not, browse and select it.(has a _d, or diff at end)
type OK to come back to the Vray material editor window.
By this time, you should notice that your material appears visually as such in your model.
Select it and scale it in the material window of sketchup.
Now, if you find how to make the pattern to start from a precise point (usefull for a glass blocks door for instance) please let me know.
Bon courage.
NPAT