Millitorrs are generally called "microns". It is assumed among refrigeration engineers that during vacuumation processes the oils in systems worked upon, themselves, do not boil - no matter how high vacuum would be achieved. I am in doubt.
PS: in the sciences we call a millitorr a millitorr ... your use of "microns" refers to "microns of Hg". I'm sure it is useful in your engineering jargon as a short way of saying what you mean, but it is certainly not a common expression.