The black cone is plastic, possibly polyurethane. They’re good pictures for gluing. I’ve done the same repair myself years ago. Preparation is everything, plus right ambient temperature.
Regards hull bladder, given yours is a MKII GR I’d say it was hypalon too. I did the repair on a Zodiac GT which was PVC. The joint fails at the transom end as it’s a thermal bond, well it was on the GT.
More details here:
http://www.rib.net/forum/f50/zodiac-...irs-52694.html
Good luck with the repair.