If I simply cut the blue wire, the fans should run at full RPM all the time, and since the miner will still receive the PWM signal from the fans, it will operate normally (won't assume fan failure and stop mining). Is this correct?
Maybe.
There are 2 control methods, one is no signal on Blue = full speed which in my book is the safest, the other is no signal = lowest speed. Looking up the fan specs should say which they are.
I've never played with the fans so just cut the blue on one fan and see what it does, you can always splice the wire back together if it slows down. Beyond that setting min fan speed to 100% - should - force them to always run full speed.