Copying evaluation board PCB layouts
I think that this situation is mostly because chip manufacturers are not particularly savvy about copyright law. You should definitely copy their eval boards as closely as possible and feel good about doing so. The manufacturers make eval boards so that you can use their chips; they're happy to have you follow their examples.

The only exception that I can think of would be if you were planning to sell the resulting board as an eval board in competition with the manufacturer. But that seems like approximately the most tedious possible occupation, so I assume that's not your intent.