I wouldn`t use fresh coniferous foliage as a mulch for anything other than calcifuges such as rhododendrons, and even then I would prefer to see it partly composted first. There are two main problems :-
(a) As you suspect, it is highly acidic - composted it usually produces a pH reading of 5 or lower, and
(b) It will take 3 years or more to break down properly (even in the soil), so what are you going to do with all the fine foliage that drops off the branches by the time you want to remove the mulch? You won`t be able to rake it off, and you don`t want to dig it in.
Properly composted it makes an excellent, if highly acidic, soil conditioner, but you really need to shred it first and compost it separately, and even then you would need it to use it with extreme care in the vegetable plot and with one eye on the pH meter.