Scorched dry kettle; still safe to use?

You didn't say whether the scorched enamel was on the outside or inside of the kettle. The outside enamel is probably ruined. I would do a really good scrubbing of the inside with something like Barkeeper's Friend before even trying to use. Is the inside enamel also? As long as it is still intact and not shedding little pieces of broken enamel, after a good cleaning it should be OK. I would also check that first potful of boiled water to make sure.