Yes, you’ll continue to get Gabriel chapters throughout the series. A lot of the secondary characters get point-of-view chapters, but he gets the most, as the second-lead character.
He also has more short fiction coming out. It’s tough to write “prequel’ stories for Olivia, because she was in a very different place—no Cainsville, no investigating, no powers. Gabriel is easier—he had Cainsville, knew something of the supernatural via his aunt’s second sight, and being a lawyer lets me have him investigate cases pre-Omens.