I think that maybe someone had the good intention of putting the metal grate on a nonconductive trough, but sounds to me like there should be a clarification from the NEC. if the grate can't move around, then wouldn't it be fixed in place ? and its metal, and its with 5 '. I can see where it can be construed as equipment. I think that you should write a note to your architect outlining the quagmire and explain to him that if he doesn't respec a fibreglass grate, he needs to contact the NEC and get a clarification (let us know the outcome !!)