Yes, graphene appears to offer a negligible improvement over other kinds of paints based on black carbon, e.g. Vantablack.
The research article linked above does not claim a better emissivity than Vantablack, but a resistance to higher temperatures, which is useful for high temperature sensors (used with pyrometers), but irrelevant for a satellite that will never be hotter than 100 Celsius degrees, in order to not damage the electronic equipment.
The research article linked above does not claim a better emissivity than Vantablack, but a resistance to higher temperatures, which is useful for high temperature sensors (used with pyrometers), but irrelevant for a satellite that will never be hotter than 100 Celsius degrees, in order to not damage the electronic equipment.