Yes it is and a design engineer should approve the extra load added either on top or bottom of the truss.
R502.11.3 Alterations to trusses. Truss members and components shall not be cut, notched, spliced or otherwise altered in any way without the approval of a registered design professional. Alterations resulting in the addition of load (e.g., HVAC equipment, water heater etc.), that exceed the design load for the truss, shall not be permitted without verification that the truss is capable of supporting the additional loading.
Commentary: Addition of loads in excess of the design load is allowed only if the additional capacity of the truss can be verified. Also see the commentary to section R502.8.2
Now, having said that, I believe it will depend on the house.
If it’s an older house and I see that the addition looked recent, then I would definitely write it up, since the design of the truss system most likely was not made for the extra load.
If it’s a new construction and I can see the plans or I see that the section of the truss over which the HVAC platform is, was reinforced or had a different truss design, then no, I would most likely not write it up, since at that point, the original design of the roof was intended to receive that extra load.