John
The insulation on the pipe in the picture is black foam insulation and is not considered combustible. I know of no special connector for joining single wall pipe and b-vent pipe. If there is such a thing I would like to see the specs. on them as most of the b-vent pipe manufactures that I have sold in my 20 plus years in the plumbing and HVAC trade do not have such a thing.
I do agree with you on the single wall pipe needs to be screwed to the vent hood, but do not agree with the screwing of the single wall pipe to the b-vent. B-vent manufacturers only allow a 1/4" screw and that can not penetrate the walls of the b-vent pipe. That being said there is no wholesale house selling 1/4" long screws that I am aware of much less a DYI store.

__________________
Well thats my 2 cents.
Brian Kelly
Kelly Home Inspections