#1
Does slipknot use a pedal to get their tone into Drop A or any other tone? Isn't it hard to find a guitar that can handle that? If they do use a pedal does anyone know which one it is?
#3
They both have signature guitars specifically designed to be put to Drop A/B/C. Other than that, yeah they're probably using pedals.

http://www.uberproaudio.com/ <--- This is where I usually go to figure out what artists are using.
#5
Slipknot uses an array of pedals, and Jim Roots rig is pretty different from Mick's. These artists do have signature guitars, but any guitar can be tuned down, you may need bigger gauge strings to compensate though however.
Treble>Epiphone Prophecy EX - MXR micro Amp - MXR Blue Box - MXR Fullbore - MXR Noise Clamp - Vox AD30VT
Bass>Ibanez BTB505 - MXR Blowtorch - MXR D.I. - Peavey MaxBass 700 - Peavey TVX410