FB bodies are useless pieces of ("Forgotten beast platinum") that cannot be interacted with in any way.
No, I'm quite positive that body parts of metal creatures can be melted. On the top of Iron man wiki page there's a mention of that. If it works for iron man, it should work for FB. Still, I never tried it myself, so I can't be completely sure.
The Iron Man monster becomes an Iron Statue item on death, which can be melted. It's a special case. All forgotten beasts become Forgotten Beast Corpses upon death, which are not valid meltable items.
The article said the severed body parts are meltable.
Slightly off-topic, but I want to clarify a bit more on this in case anyone wants to mod in metal creatures. Any creature with a body part whose tissues are made of metal can have that part melted into bars. There is one slight trick to this, if you are modding, though. Make sure the tissue material is the actual metal, not a material based off the metal.
Using iron bones for example:
[USE_MATERIAL:BONE:INORGANIC:IRON]
[TISSUE:BONE]
[TISSUE_MATERIAL:LOCAL_CREATURE_MAT:BONE]
This would be wrong. Trying to melt the bones would probably yield <creature> bone bars or something(I haven't tried it). However:
[TISSUE_MATERIAL:INORGANIC:IRON]
This would make bones that can be made into iron bars.
What I am uncertain of is whether or not FBs made of metal use actual metal in their tissue mats, or whether their tissue mats simply [USE_MATERIAL]. If it's the former, and the entire body is made of the same material, then yes, they can be melted into bars.