Couldn't he gamble with them? Put one or two chips down at a time, keep the winnings as "clean" chips and gamble with the dirty ones until they're all gone?
Sure, I'd imagine so. However, just waltzing in and not visiting the counter for exchanging cash for chips might seem odd. Easily taken care of by bank rolling your trips with some real money and "peppering" in your stolen chips.
Also, I'm just guessing what he looks like under that helmet, but I'm guessing your typical armed-robber type wouldn't fit in well at the high roller table.