Oh yeah, they're definitely looking to hide more serious transgressions:

The White House yesterday hinted that it may try to assert executive privilege in denying Congressional investigators access to e-mails sent and received by White House aides on their Republican National Committee e-mail accounts.

It would be an unconventional exercise of a privilege that is controversial even in its traditional application: to protect the White House itself from subpoenas. And it would be another twist in an already peculiarly convoluted story.

In what Democrats suspect was an attempt to avoid public scrutiny, some key White House aides violated internal policy and potentially federal law by using their RNC e-mail accounts (instead of their official White House e-mail accounts) to conduct official business. Once the use of those accounts was exposed, the RNC announced that many if not most of those e-mails had been deleted. Now, the White House is saying that should any of those e-mails somehow turn up, they should not be turned over to Congress without the White House's approval.

[from Dan Froomkin]

And make no mistake, they have the emails but are stalling for time. It takes some doing to peruse through millions of emails, choosing which ones to hold back and then redact the others like crazy.

Oh, and can we please stop calling them "document dumps," implying indiscriminate mass unloading of info? They're anything but that.