Paint for that time depending if it was made in a field or shop is not untraditional. Though the paint they had did not come from a spray can, it was more like house paint.
As far a fire grate, I will paint them if it is for a customer. It looks alot nicer and gives the apperance of more time and care being put into its' being made.
Use krylon high heat paint. The campfire will never reach the temp to burn it off and does not affect the safety of cooking. After the continual use of the grate in the fire will help protect the grate.