I asked a couple of other experts ... and here is what I've gathered.
1.5 Typeforms [UEB manual] says: <br clear="none" />In mathematics, algebraic letters are frequently italicised as a distinction from ordinary text. It is generally not necessary to indicate this in braille. However, when bold or other typeface is used to distinguish different types of mathematical letters or signs from ordinary algebraic letters, e.g. for vectors or matrices, this distinction should be retained in braille by using the appropriate typeform indicator. See Section 2.7 for the emphasis of individual digits within numbers.
We would take this to mean that just as bold is required to be retained for vectors, the italics should be retained for scalars...but is not required on other letters. If you cannot tell which letters ARE scalars (I, for instance, might find that difficult), I would ignore the italics on all letters and put a TN under the statement in the physics book (as you suggested above).