Sentencing is April 23 for Dennis, who faces up to 20 years in prison.
Dennis was indicted in June on charges accusing him of selling iPhones and other electronics to online shoppers without delivering the merchandise.
Investigators say the $132,000 fraud involved at least 29 individuals since September 2008. Dennis, who is free on bond, must make restitution.
Dennis was the lead member of the gangsta rap Geto Boys, who recorded hit songs between 1989 and 1996.