No question about it. The order of events according to Boeing is that the speed brakes are first selected manually in order to dump the lift. The back up action in case the manual action is inadvertently forgotten is that when reverse is selected it will also actuate the speed brakes.
If the abort is due to a fire warning in an engine, then depending on the severity of the fire, it would be unwise to select full reverse on a burning engine. In any case, by the time you have got through the interlocks into meaningful reverse, the RTO action would have reduced your speed into the area where the retardation of reverse is nearing minimal. Thus it is vital to immediately select manual speed brake as part of the immediate abort actions.