How is Wikinews different than this situation? The problem with Wikinews in this sense is that there are no "leaders" or editors-in-chief who can take the legal arrows, so to say. In this case I think it would be more the administrators who are maintaining and verifying the credentials of Wikinews reporters who would have the legal liability.
Not necessarily something pleasant to think about for that matter, and dangerous in a volunteer organization. Certainly something to discourage you from becoming an admin on Wikinews. Having the Wikimedia Foundation take the heat instead would help insulate the admins and others on Wikinews but opens up other issues as you have suggested. The real question then is who has the certifying authority and who has the liability for the problems? The two go together.
There is a need for accredited reporters, as there are some news media events that can clearly be covered only by accredited press members. In the USA in particular, the government has no role in the accreditation process and instead it is from the authority of the news agency they are working for. This is the real meat of this issue, and to decide on how the accreditation will happen.
BTW, I was turned down from one media event already where I tried to cover the event as a Wikinews reporter but lacked credentials. There will be other opportunities in the future, but this is a real situation.
Maybe one solution would be to become some kind of Non-Governemental Organisation, or to create local comitees. Anyway, we need to think about it !