I think you may need to go back to the folks at the Navy med research branch and get some more feedback on treating hypothermic victims. The best way to treat hypothermia non intrusively is to warm the air the hypothermia victim is breathing in. Having a second person together with the hot water bottle in something like the Blizzard Tube (an effective vapour barrier) is to warm the air inside the Tube itself. The warm moist air generated by the fit healthy crew member will then warm the victims lungs/thoracic part of the body and will help speed the warming of the thermoregulatory part of the brain called the hypothalamus. This will more than compensate for the effects of dilating peripheral blood vessels.
Getting the victim out of cold wet clothing is just as important and this will dramatically reduce the heat loss due to the wet clothing. Rapping the victim in a simple space type blanket will just not work with air temperatures below 10-15 degrees Celsius.
This is why all UK arctic warfare unit members are instructed to keep a spare set of clothes in a dry bag in case of immersion in icy water.

As you have mentioned a hot drink does not look possible due to the HAZMAT regulations despite the fact that gas cartridge failure rates are extremely low compared even to lithium battery incidents. Could the hypothetical hypothermia kits be deployed separately from the deployment of the life rafts?

A good guide to treating hypothermic casualties is available at http://www.hypothermia.org/Hypothermia_Ed_pdf/Alaska-Cold-Injuries.pdf