They'll only have a problem if you don't label your units or say somewhere what they are. And if you don't do that, that isn't an imperial vs metric problem, that's flat out bad engineering.

Um, they wouldn't have a problem with that. That's exactly what I used to do, fabricate steel parts for companies like Liebherr and Komatsu, who would send us blueprints in metric. My coworkers and I actually preferred it.