The former first baseman with the Diamondbacks and the Chicago Cubs was fired after he was arrested last August in Scottsdale -- his second drunken driving arrest in 15 months.
Grace has pleaded not guilty in October to four felony counts of aggravated DUI. His trial is scheduled for March 19.
Though the Diamondbacks fired Grace after his most recent arrest, the team invited him to participate in a fantasy camp now under way in Scottsdale.
The Arizona Republic quotes Grace as saying he was "happy to grab that olive branch."
Diamondbacks president Derrick Hall says the team supports Grace and looks forward to his future involvement in the organization.