Plastic welding is often used to repair cracks in single-layer, linear polyethylene canoes and kayaks. The Ram-X material is a three-layer rotomolded PE material with a foam core. What is more, it is described as "cross-link thermoformed high density polyethylene".
There are two chemically distinct varieties of polyethylene used to roto-mold canoes and kayaks, linear and cross-linked. Linear polyethylene can be thermally welded. Cross-linked polyethylene (using that term in the correct chemical sense of the word) cannot be repaired with thermal welding. If you try to the material will not melt but simply spark and burn.
Having said that, I believe that Coleman and Pelican are not using the term "cross-linked" in the correct chemical sense of the word. I believe they are referring to the foam core which is "cross-linked" to the two outer solid layers of PE. I could be wrong about that, but I believe the Ram-X material is high-density linear PE.
If so it can be repaired with thermal welding but the trick will be dealing with the foam core. It will be easy to melt. I have heard of folks using thermal welding to repair three-layer roto-molded PE and Royalex hulls, which also have a foam core. But it is not often done and I believe would be best left to someone with experience repairing that type of hull with thermal welding. Unless of course, you are not too heavily invested in a successful outcome and just want to experiment.