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 of "Permissible Sprinkler Omissions" in both the Uniform Fire Code and Uniform Building Code.
UFC1994 S1003.4 UBC1997 S904.4
Rooms containing electrical equipment are NOT considered
a permissible omission.
