Can Spray-foam Insulation be directly applied to Push-Fit fittings?

No! The fittings must be protected against direct contact with the SPF insulation by wrapping the fitting(s) with silicone pipe wrap. The same precautions must be taken when installing in areas where contact with primers, solvents, solvent cements and firestops. 

Can Spray-foam Insulation be directly applied to plastic piping?

Maybe, it is the sole responsibility of the installer to verify with the pipe manufacturer to ensure that direct contact with SPF insulation is an acceptable practice and that the pipe's warranty will not be negatively affected by doing so. Different brands and types of plastic pipe may not allow the SPF foam to come into contact with the pipe. 

ADDITIONAL RESOURCE:

Plastics Pipe Institute (PPI) provides recommendations for safe installation of SPF (Spray Polyurethane Foam) on and around plastic piping materials and offers the following procedure when applying Spray-foam insulation to prevent damage to the PEX piping. Note that newer closed-cell SPF formulations using HFO (hydrofluoroolefin) blowing agents may use different catalysts which, in some foams, can increase the peak temperatures during curing to as high as 325°F [163°C].

https://plasticpipe.org/common/Uploaded%20files/Technical/TN-69/PPI%20TN-69.pdf

4.0 RECOMMENDATIONS FOR SAFE INSTALLATIONS OF SPF ON AND AROUND PLASTIC PIPING MATERIALS

To avoid excessive temperatures, Do Not encase plastic pipe and fittings in a single pass of SPF.

SPFA recommends that when there are plastic pipes in a wall, ceiling, or floor cavity, the SPF installer should apply one layer of foam until it touches the pipe but does not encase the pipe. SPF installers should let the first layer of foam cure for a sufficient amount of time while the heat is released, and the pipe remains partially exposed.

Typically, this is when the surface of the SPF has cooled to approximately 100°F (38°C). Then, they may apply the second layer. This way, the pipe is never in the middle of a thick layer of foam insulation during curing.

The first layer of SPF insulation is stopped when it reaches the pipe, just barely touching or encasing it, but keeping portions of the pipe exposed. After efficient cooling time, the second layer of SPF insulation is sprayed over the pipe to the required thickness. If pipes are installed at different depths, continue this process for each depth of pipe. This is the correct procedure. 

Installation of pipes and fittings within a single pass of SPF is not permitted as the temperature within the foam may exceed the capabilities of the pipe and damage pipes or fittings.