If someone is having a wall oven installed, should the racks that come with the oven be toveled as a separate item? Note that racks of this type can be removed from the oven.
Practically speaking, no food is ever placed directly on the oven rack save for bread to be warmed or toasted. As such one can rely on Rabbi Moshe Feinstein who says in his Igros Moshe Yoreh Deah 3 siman 24 that toasters don't need tevila being that you are not cooking or preparing the bread, but rather just drying it. And while its true that this drying is what makes the stale bread edible, it is still not called cooking.
If there is some other case where food is put directly on the grate, a different answer will apply.
But contact your local orthodox rabbi.