A8.15 allows "any unit" to make Small-Arms/MG Defensive First Fire attacks to claim a Snap Shot if its prerequisites are met. This is the rule that "allows", which means in principle, the answer is "yes".
"A8.15 SNAP SHOT: Any unit wishing to make a Small-Arms/MG Defensive First Fire attack may claim a Snap Shot if it can trace a LOS to an entire hexside (even if that hexside is part of a Blind hex) that was crossed by the moving unit in entering a on-board hex (even if the center dot of that hex is out of the firer's LOS) [EXC: A Snap Shot cannot be taken at a unit while entering the firer's hex]."
Then we continue to look if under specific conditions this permission is revoked (i.e. disallowing) and we find these later in A8.15:
"Neither a MG that must change its CA (9.21), nor an ordnance weapon, nor a weapon using IFE/Canister can make a Snap Shot (see also B9.2 and C.5)."
So "any unit" making "MG Defensive First Fire attacks" (I don't see why this "any unit" would not include vehicles) MINUS those in which "a MG must change its CA" are permitted.
von Marwitz
You might be right, but if "MG" and "Vehicular MG" are two different things as they appear to be in the Index than Vehicular MG are not included in A8.15.
Also you have confirmed that the description "a vehicular MG" has been specifically
removed from the Second Ed Snap Shot rules. Why remove this reference if Vehicular MG are in fact allowed to use Snap Shot? Also you are insisting that the rule for MGs with ROF (A9.21) apply to Vehicular MGs, which do not have ROF. Why not also refer to the Chap C/D rules on changing CA, if Vehicular MG are meant to be there?
Considering those details I am seeing nothing in there which allows Vehicular MG (assuming separate to MG as per the Index) to use Snap Shot.
Perhaps removing the First Ed comment from the Second Ed was a mistake, and perhaps not using the phrasing:
"
Any unit wishing to make a Small-Arms/MG/Vehicular MG Defensive First Fire attack may claim a Snap Shot"
was also a mistake.
I can see how mistakes happen and perhaps it was always intended in Second Edition that this use of Vehicular Mg was allowed, but it certainly isn't clearly the case.