Can I fit a 32-630 tire on a 20-622 rim?
No.  The bead seat diameter (inner diameter) is different by 8 mm.  You cannot shrink a steel or Kevlar bead by 8mm, as they are designed not to stretch  or shrink (otherwise a clincher tire will roll off the rim in a corner).   You can try but the tube will burst out from the extra space. 

The tire bead is what interfaces with the rim.