It depends on where the AHJ is located. For instance in Indiana, the AHJ can require it. The Indiana electrical code has this definition:
(a) In Part 1 of Article 100, delete the text of the definition of APPROVED and substitute to read as follows: APPROVED. Acceptance by the AUTHORITY HAVING JURISDICTION by one (1) of the following methods:
(1) investigation or tests conducted by recognized authorities; or
(2) investigation or tests conducted by technical or scientific organizations; or accepted principles.
The investigation, tests, or principles shall establish that the materials, equipment, and types of construction are safe for their intended purpose."
In some areas, the AHJ can require everything to be listed.
If Information Tech. Room is being made to meet the requirements in Art 645, then all the Information Tech. Equip. in the room has to be listed as I.T.E. to meet the requirements to take advantage of the modified wiring methods permitted in Art 645
On second glance the Code (at least in 99) does not say all equipment, just that "Listed information technology equipment is installed."
At any rate my guess is this is the code section they are referring to. 645-2(c)
errol, I at one time was a rack designer in SV and the caveat for listed equipment was basically rooted to the cabinet and its interface rack structure and instrumentation drawer power strip configurations. Any custom variations required UL, CSA, etc listed or labeled components prior to installation acceptance. Any of this sound familiar?