Looking as Simulator output, it looks like the Shadow Thrash artifact trait does not get the 10% crit from the Tier 1 Blood Scent Trait. See: report.
I haven’t gather in-game data myself, but looking at logs (example1, example2 WCL id: x1jCyp2dPZR8FXD6) it looks like Shadow Thrash Crit rate is closer to abilities affected by Blood Scent (such as Rip/Rake/Thrash) than it is to unaffected abilities (melee, Old War). Simulationcraft does apply the Crit effect to Shadow Thrash as well, but I have not tried to collect in-game data myself as of yet. Overall effect is likely immaterial on overall results, maybe ~0.05% dps.