Hard to say.
If the alloys of the keys (or whatever else occasionally gets "buffed" on that machine) contain lead compounds... and brass alloys often do....... then the lead is almost for sure fuming out of the glaze at cone 6. Those fumes (fumes are tiny particulates... not gases) are depositing on everything in the kiln..... the other glazed areas of the same piece, the posts, shelves, the pots not even glazed with the key shavings, etc. And if the kiln vent is not holding a negative pressure on the chamber... are leaking into the room.
How MUCH of this is happening........??????? Lacking accurate lab testing of the raw material or the fired products... you and I and others don't know. Is it huge amounts of lead fumes produced? Almost for sure not. Is it enough to be a potential problem? Maybe... maybe not.
When you are working this way it is all a lot of question marks.
To me that Oribe-type glaze looks perfectly reproducable using materials form a ceramic supplier. Those commercial materials are relatively chemically pure...... and I can get a typical analysis of them. They are intended for use in ceramic process. Key shavings are not.
So the question for me then becomes .... why use the key shavings which very likely might have some "questionable" content? I can immediately see four potential answers ... or a blend thereof:
One..... the key shavings are free ...so money can be saved on supplies.
Two...... the key shavings are getting recycled so it is doing "good things" for the ecology/planet/etc.
Three..... it produces visual results that can not be gotten any other way.
Four....... using local non-traditional materials provides enjoyment and challenge.
The potential negatives that I readily see are:
One........ it is possible that the glaze has some toxic components that could be leaching out.
Two...... if there are toxic components, they may be potentially harming the users of these products... likely very slowly.
Three...... there is legal responsiblity for any harm caused by products produced.
Four...... the material is not intended for use in the manufactuire of such products, so defending its use in the case of problems will be difficult.
Five...... firing the materials may be slowly contaminating the kiln, shelves, posts, and the studio environment.
Six.... there is no accurate information about exactly what this raw material is chemically.
How these concepts all "balance" each other is what you probably have to weigh for yourself.