As it seems to dwell constantly on battles & military things I think it would be a very good preparation! It was fairly common to use the Gallic Wars as the first text to study in Latin for many years and D'Ooge would no doubt have had this in mind when intoducing the vocabulary and other material. It's not like Greek where there are different dialects etc. and Caesar wrote in a nice plain style.
Once you get through the first stages of grammar, see if you can find any brief translation pieces of Caesar in "First Reader" type books, then look around for a good, modern annotated edition of the Gallic Wars and see if you can make some sense of it - even if some parts are beyond you.