Hilzoy digs through McCain's record:
Short version: during the last four years (all I checked), McCain has supported basic appropriations for vets. However, when there are two competing proposals, he generally chooses the cheaper one, and often, when only one proposal to increase benefits is available, he opposes it. But, as Beutler says, this doesn't seem to be because he is in general in favor of fiscal discipline: in 2006, in particular, he voted against several bills that actually tried not just to increase spending on vets, but to pay for it, in one case voting for an identical bill that was not paid for.
Should Obama pick Webb as a veep, this issue would become salient. Otherwise, not so much.