Experts can be found in many organizations. As a Greenpeace spokesperson points out, the report also includes an author who is from Chevron as well as researcher from Exxon.
I highly suspect that Mark Lynas is wrong to write that Greenpeace "dictated" the report. I've heard many people talk about their experience working on an IPCC report and no one seems to dictate anything -- every sentence is gone over with a fine-tooth comb and endlessly hashed out. Unless someone has some good evidence that Sven Teske had some special influence in constructing the report (and nothing Lynas offers indicates that), this is once again a vastly overblown issue.
This is hardly the equivalent of a Dick Cheney-like situation huddling with oil industry representatives to divide up the Iraqi oil fields.
As Andrew Revkin writes, the IPCC should have been more transparent in their press release. But they should take expertise where they find it, and nothing says Greenpeace or any NGO can't have that. In fact, I've met more than one person from NGOs who knew as much about an issue and had done as much detailed research into it than so-called experts.