is it Boeing standard that the ELT is located in the aft galley?
As a rule, the transmitter unit will be as close to the antenna as possible (just slightly forward). The longer the cable run, the more you have to worry about the antenna cabling being broken in a high G accident. The aft galley would be a most unusual location, because the vertical stabiliser is over the galley. The ELT antenna has to be well forward of the stabiliser.
The instructions in one 737NG AMM for servicing the transmitter unit mention the removal of sculptured ceiling panels in the cabin. The location is given as station 770, which is about 6 windows from the aft door. The antenna is at station 797 (27 inches aft of the transmitter). Another airline's 737NG AMM shows the transmitter unit at station 794 and the antenna at station 795.6.