Steve Harvey hosts Essence magazine's 15th annual gala, taped May 31 in L.A.. Diana Ross, Roberta Flack and Melissa Etheridge are slated to participate in tributes to such honorees as Halle Berry, Janet Jackson, Alicia Keys and India.Arie. Also scheduled: appearances by Samuel L. Jackson, Heather Headley, Angela Bassett, Kelly Price and Jaheim.