Did a test and shield depleters works nicely on fighters. I didn't know that  
 
 
One stack of 25 fighters with a total of 1500 shield points:
- Takes 5 hits by a Large SD-5s to tap all shields (5 x 300), as expected.
I build an ETL and tries again:
-  Same 5 hits still taps all the shields. 
So it seems like ETL's don't work on fighters at all  
 
 
Did the test with sequential moves and tactical combat, dunno if that makes a difference.