1 cubic foot of 2# foam weighs 2 pounds. 10# would weigh 10 pounds per cubic foot. The higher the weight, the more dense it is and the stronger it is. Unless you know the exact weight of the foam and the thickness of each type, as it was engineered by Hot Spring Spas, I would surmise a high chance of failure and your spa will wind up cracking beyond repair.
There's at least one jet that's malfunctioning. The jets are designed with a built in venture, which will naturally pull air through the pipes you see. Could just be some internal blockage in the jet nozzle or some other debris caught in the jet. No check valves are needed or intended.
Hot Spring Spas isn't lots of spas. Again, I believe the foam is an integral part of the structure and without it the shell WILL crack. Additionally, the foam is layered on in different, specific densities, to give it the overall structural support.