When using linen thread I cut a stitch grove. Back in the day, I used a marking wheel and awl for the hand stitches down the stitch grove. Today, with the high tensile, tough thread, like Rita Tiger Thread, I'm not cutting a stitch grove, I mark a stitch line with my dividers and predominately use my diamond chisels to cut the stitch holes. Depending on the project, the old awl still has it's moments. No reason you couldn't cut a stitch grove to sink your stitches below the leather surface, and then use the diamond chisels to cut the stitching holes.