Correct. Blipping it at the wrong time does you no good. To do it absolutely perfectly, the throttle needs to be increased as it approaches the KE positions. Go to http://www.flyinggiants.com/content/groundschool.aspx (you have to be registered) and watch the "rolling with Leseberg" trailer and watch his left thumb carefully. You will see the throttle increase as rudder is applied. It is very slight in this case, because the harriers aren't very high alpha, AND because both of those planes are electric. Yes, that Dalton 42% 260 is electric! Gassers typically require a little more input.
However, harrier rolls don't require this, they are just smoother with proper throttle input.. To learn them, first worry about correct rudder and elevator inputs.