Hi Lane,
Wikimedia DC does not currently carry an insurance policy.
That having been said, there are a couple of points that I would recommend you consider in your case:
(1) The regulation you cite seems to be about general liability coverage (which typically applies to things like personal injury, etc.). This is normally not the same as either errors and omissions (E&O) coverage, which in my experience is typically of interest only when the organization is performing some sort of professional services (and could be sued for performing those services improperly) or directors and officers (D&O) coverage, which is what protects individual members of your board from liability if you're sued for fiduciary misconduct, etc. I would suggest clarifying with your local regulatory agency whether they are in fact only talking about general liability coverage here; while I suppose it's possible that some quirk of Washington law would allow that to be applied to other scenarios, it does strike me as rather odd.
(2) Generally speaking -- and, again, without having looked into whether some aspect of your local laws mandates certain actions on a statutory basis -- the question of whether an incorporated nonprofit carries insurance coverage is distinct from the question of whether that nonprofit indemnifies volunteers against liability related to the performance of their duties. It's possible, at least under DC law, to do either one without the other; in other words, we could indemnify our volunteers without carrying insurance coverage (in which case the organization would be directly responsible for paying any damages) or we could carry coverage exclusively for the organization's benefit, without necessarily indemnifying individual volunteers. I would suggest checking what the statutory provisions for this are in Washington, but, regardless, I expect that you will want to have something more detailed and explicit about this in either your bylaws or some additional policy. Note that you may not necessarily want to offer a blanket indemnity to everyone who might claim to be a volunteer, since you may have no knowledge of or control over what they do in that capacity.