A spoiler with a "tight" hydraulic actuator (not bypassing or leaking) will maintain its last commanded position.
It takes all three (electrical power, hydraulic pressure, and the handle being moved into down position before they lower themselves. I guess you could lower the handle first, but I would think safe work practices are the reason why Boeing placed the procedural order as they did.
Most mechanics, upon hearing the hydraulic pumps come on are going to pull their hands (arms, legs, body) away from any flight control. If the spoiler handle was stowed first..... as soon as pressure hit..... they would slam down, giving a mechanic in harms way no time to react.
It is a known rule "not" to apply hydraulics until everyone near (on/under) a aircraft has been informed.
I would be leery to be around a spoiler (even with the actuator lock installed) with hydraulics on.
Actuator valves do leak. I've seen spoilers up with the handle down just off of accumulator pressure. I've seen spoilers come down when selected up without hydraulic power. Most mechanics are going to safety tag flight control handles and pull the hydraulic pump breakers before work starts.