You probably do not have a choice in the matter as to participation.
As far as I know, it is a policy that only applies to work done on a specific project and whatever liability the project might end up having, as opoosed to a typical liability policy that you would have as an EC.
I think the idea is to avoid the finger pointing that goes on if something bad happens. The wrap up policy covers the incident and the insurer goes after the insurance company of the guy who is at fault so the owner does not have to do so. It also makes sure that the appropriate coverages are in place for the owner.