For the non linear restraint, the stiffness is a function of displacement, in the sense that if the pipe touches the support the stiffness is the default stiffness or else it is zero.So a one word answer to your question is no.
For Frictional non linearity, the concept of default stiffness does not change, however the analysis method is little bit different ( you can read about the same in the Technical Reference manual in tecchnical discussions).

To know more about hangers , again read technical reference manual ( technical discussions).

The origin of the method of using high stiffness springs to model restraints can be found in any standard text book on Finite Element Method or Structural Analysis, which I would advise you to read.

Regards