Yes sprinkler heads are "allowed" to be installed in an electrical closet. For many years certain areas have not had heads installed, due to the electrical question. Today even elevator rooms are sprinklered. ANSI and other groups are still working on that detail.
There is a list...
You may wish to check the Uniform Building Code.
905.10 Control Air Tubing.
This section would disallow poly if your application is governed by this code.
Similarly plenum cable is disallowed under section
905.9.2 Wiring.
I don't know the building code used in your location contains similar...