Here comes an assumption...
During an Emer Evac, you will be left on batteries only, correct?
So, I checked the Elec Emer. Config Sys Remaining on the QRH, which says:
Taking a look at the FLT Controls Architeture, we find that spoilers 3 & 4 are controlled by SEC 1.
So, I'm assuming that when SECs 2 & 3 lose power, a retraction command is sent to the spoilers, but how can spoilers retract if the Hyd Fire Shutoff valves are closed (as the fire PB are out)?
Maybe they retract using some residual hyd pressure left in the system?