Similar to but different from this question, do cooling racks need to be toiveled?
According to Star K (here), metal cooling racks need to be immersed without a blessing.
According to OU Kosher (here), they need to be immersed with a bracha.
The Agudah (here) writes they need immersion with a blessing if you put food on the racks, and no immersion if you only put pans on there (but that requires certainty you won't ever want to put food directly on them).
So you can either ask your friendly local Orthodox Rav for his ruling, or you can first immerse a utensil that definitely needs a blessing, then immerse the cooling racks.