Eval designs are rarely copyable because your design will usually have many additional components that impose many more layout constraints than the eval board designer had to deal with.

There is a distinction between evaluation boards and reference designs. Manufacturers will provide Gerber files for the latter, so that they can be copied exactly.

You should definitely copy PCB manufacturer's eval boards as closely as possible. The manufacturers make eval boards so that you can use their chips; they're happy to have you follow their examples.