I have never heard of this generalization. If you review SA-307, section 4.5 there is specific reference to zinc coatings both hot dipped and mechanically deposited for fasteners. See ASTM A 153, this is one of the stated reference documents.
It is not true that SA-307 bolts cannot withstand galvanization.
Clause 4.5.1 of SA-307 of ASME Section II Part A states as follows: -
When zinc-coated fasteners are required, the purchaser shall specify the zinc-coating process, for example hot dip, mechanically deposited, or no preference.
