It's definitely safe
...metal won't burn or really do anything but get hotter till it gets to an incredibly high temperature, and the metal doesn't heat up enough hotter than the air temp of the oven to be a problem for touching the clay.**
In fact, most materials are fine to put in the oven with polymer clay since the curing temps for polymer clay are so low. But since the melting or shrinking or burning temps of plastics vary from about 200 to about 300, there are some plastics that won't work with clay or that will work but only in certain ways (as one example, polystrene foam shapes can be wrapped with aluminum foil then used inside the clay as an armature, or they can be left bare and will shrink inside the clay after the clay has hardened at least some in that shape).
All kinds of metal things are used inside or on top of or partially inside polymer clay... tightly-scrunched aluminum foil is often used as an armature when sculpting for instance, or metal eye pins (often with shanks bent) can be inserted into raw clay and baked with it, and other kinds of metal wire/mesh/sheets/rods are often used inside or through or embedded, etc.
Some materials will expand or contract with heat though, or just quicker than polymer clay will, so there are a few occasions when glass or metal or bare wood could be a problem if completely
covered with clay... generally slow cooling
will take care of that though....and in the case of bare wood, which will probably contain some residual moisture, it should always be sealed with acrylic paint or white glue, etc., before having clay put on it anyway to prevent any air bubbles in the clay when it's heated that the moisture might cause when it turns to steam (or sometimes just oven-drying is enough).
There are a lot of pages at my site that deal with the materials and items that can and can't be used with/in/on polymer clay because of of the heat of curing (or have to be used in certain ways).
Here are some of the main pages where that would be discussed:http://www.glassattic.com/polymer/covering.htmhttp://www.glassattic.com/polymer/armatures-perm.htm http://www.glassattic.com/polymer/armatures-temp.htm
(dissolvable or removable materials, but not counting eggshells which can be later dissolved with vinegar and are discussed on the Eggs
...and maybe the Glues
pages if you're concerned about those materials when heated at our curing temps
**there can be a problem occasionally if a metal baking sheet is used as a direct baking surface for the clay and it's a little too close to the bottom coils... in that case the metal can heat up a little higher than the air and so cause some of the clays to darken from that excess heat (again, easy fixes though... just put the clay on paper or a tissue or fiberfill or baking soda or something else to keep it from being quite so close to the metal pan; and btw, any place a very smooth
material touches polymer clay while it's heating or cooling, that spot on the clay will become shiny because clay will always be a bit soft while hot and so will take on the "texture" of anything it's touching)