If you're talking about the AT IO crit procs, the Scrapper's Strike Crit Bonus is passive and can be slotted anywhere, doesn't need to be activated. I have it in Swipe as the only slot/enhancement, for example, and swipe is never in my power tray.
The Critical Strikes +50% Proc, however, must be activated. I've got that full set in Followup so that when it fires off, I'll have a much higher crit chance on focus and slash.