From your description, I'm sure that it is possible to write a script that suits my purposes (that is not primarily gray literature). (realclimate.org)
I think it's OK to cite gray literature, as long as it merely fills in the gaps or adds supporting evidence to what is already well established. (wattsupwiththat.com)
IPCC in many places copies entire paragraphs without attribution from either the work of its authors or of various sources — often gray literature like Greenpeace or WWF reports. (climateaudit.org)