Regarding the Hashishin, in STW you had a equivalent unit in the form of battlefield ninja's: 12 men armed with swords and shurikens.
If the AI had them, I could see them moving, but I couldn't target them until they were quite close. Since the AI used them incorrectly (in the few cases he had them), this was not a problem. When I used them, I found that the AI actually ignores them until he accidentally stumbles onto them or if they open fire. But anyway, I never got much use out of them. They couldn't even kill an ashigaru general