As reported by Michael Sanserino on twitter. Gomez will start today against Seattle. He's been on the DL since June 3 with inflammation in his right forearm.
The other possibility to be sent out was probably Ryan Reid, who has all of his options left. The Pirates are probably more in need of a pitcher who can go multiple innings, especially since their late-inning relievers are well rested right now. Reid may fit the middle relief role better because his control is better than Welker's.