I would say that since it's only markup and doesn't affect the look of the site like CSS, it doesn't matter, unless you would use the same id's and the same cla

I would say that since it's only markup and doesn't affect the look of the site like CSS, it doesn't matter, unless you would use the same id's and the same classes but still, look at all the grid frameworks,they use the same classes. It's different when you copy CSS but html, I don't think it's bad at all.