Is the Bleed/ Inlet Tube necessary for a vac distill?...
Not if you use rapid magnetic stirring to prevent bumping (superheating) of the liquid. The capillary inlet for vacuum distilling is rather old-school, and magnetic stirring really is the go.
Zubrick says it is not needed if boiling stones or a stirbar is used
Boiling chips generally don't work well with vacuum, as the air which acts as a seed for vapour bubbles in the liquid gets sucked out.
for a simple distill he says to leave the vacuum adaptor open to the air "or the whole thing will explode"
For atmospheric distillation (a.k.a simple distillation) the distillation apparatus should be open to the atmosphere. Sealing it will cause it to pressurise as the liquid heats, hence the warning.
now I know a vacuum means the abscence of air, but won't the whole thing explode here too?
No, it won't explode. The vacuum pump keeps the pressure inside the apparatus low, hence no pressure can build up, so no explosion.
...Also, if needed, how open should the screwclamp be?
If you really must use a drawn out capillary to prevent bumping, then you adjust the screw clamp so that a thin stream of bubbles enters the liquid. Vogel suggests it takes practice to draw out a capillary tube to the right diameter.