In Chapter 2, Nick describes the journey from West Egg into a desolate area he calls the "valley of ashes," which could just as well be called the place of forgotten dreams, the location of George's shop. Nick describes the shop as "unprosperous and bare" and describes George as follows:
It had occurred to me that this shadow of a garage must be a blind, and that sumptuous and romantic apartments were concealed overhead, when the proprietor himself appeared in the door of an office, wiping his hands on a piece of waste. He was a blond, spiritless man, anaemic, and faintly handsome. When he saw us a damp gleam of hope sprang into his light blue eyes.
From this and other descriptions of George, I would call him a functional materialist which means that in his current situation, he does what he has to do to make a living, spending little effort trying to achieve some ideal dream. His wife bosses him around (which he meekly accepts) and she cheats on him. George seems quite defeated, a hopeless materialist. But that "damp gleam of hope" indicates that George was probably, at some time in the past, an idealist; someone seeking the ideal that is the American Dream. The American Dream can mean different things to different people. In this novel, it can be love (for Gatsby), prestige (for Tom). For George, it might mean something more practical such as a successful business (his was not) and a faithful wife (his was not). When George kills Gatsby, thinking he was responsible for Myrtle's death, he is acting out of grief but one could also argue that he is acting out of a larger frustration at being unsuccessful in life.
George is a materialist but it stands to reason that he was once an idealist and still clung to a "damp gleam of hope" which makes him both: a materialist with a faint trace of idealism from his past.