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?
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.
People just don't show up at a pedestrian craps table and throw down $25,000 chips, much less $1000 chips.
There were probably a very small amount of > $1,000 chips at a craps table anyway, and their only real use would be to pay out to a big winner.