If, by materialist, you mean that Einstein believed the laws of nature were constant throught time, and therefore subject to discovery through science, then I suspect he was.
Materialist in contrast to supernaturalist, someone who believes that the laws of nature are suspended at the caprice of demiurges.
Well jeepers, js1138, if that's the definition of a "supernaturalist," then according to your way of thinking (either/or), I must be a "materialist."
I believe that the laws of nature are universally operative and absolutely consistent throughout time. Which is precisely what I would expect, given their divine origin.