First, Begala acknowledges that he "quiped" without first looking into the details and thus made a mistake when he insulted the "nose-picking" organizers in Utah and Mississippi. Second, Begala says that he looked further and found out that the state organizing campaign is not the source of the problem. Finally, he says that he doesn't know where the extra $45 million has gone.
Did Mr. Begala bother to call up Dean and ask him?. To quote Mr. Begala, "I have no idea". Begala gives no hint that he made any such attempt. He only references (but does not link to) a Washington Post report about increased spending on consultants.
I suppose I could call up Mr. Begala and ask him if he ever asked Dean, but I'm just a "desktop campaign manager-wannabee" so I'm not likely to get through. He, on the other hand, can probably get Dean to return his phone call in short order (that's one advantage of being an insider).
If Begala has concerns about where the money is going he should take it up with Dean. If he doesn't get a straight answer from Dean he should take it up with other insiders. If he still doesn't get anywhere with it, then and only then is it time to escalate this to a public issue.
Otherwise, Mr. Begala is engaging in is rumor-mongering and deserves to be criticized for it.
Addendum: There's some good discussion on this going on in this DailyKos diary.