Dear Mulligan,
You asked, <In the event of a rudder hardover due to jamming of the servo
valve, will removing all hydraulic power alleviate the situation and
result in the rudder "slipstreaming"?>
The short answer is yes. But as 'Tcas Climb' says "Sounds like the procedure you have explained is time consuming. Did theese boys have time to do it?".
If you have a rudder hardover at below 'crossover' speeds the A/C is on it's back in a very short time. This will obviously be irrecoverable on the approach.
Regards
Exeng