I always thought open meant that you could use whatever they provided in your project. If they provide the schematic, that what you can use. If they provide the CAD files, then you can use them. Whatever they provide is fair to use. If you carry this too far people will be expecting you to provide the software to read the CAD files, the computer to run it on and a person to type in the commands.
Take what they provide in the spirit they provide it.
But this ignores Lefty's point about the license, which is more important, when it comes to acceptable use. The parallel in the world of software is disclosure of source code under a non-disclosure agreement, which is quite common. And, continuing to attempt parallels, in the world of "open source" software, there are myriad licenses, and some dispute about what constitutes "open". However, some people have worked quite hard to set up definitions, which, even if they aren't universally accepted, provide some commonality which has found significant usage. See the Open Source Initiative
. And then there's the Free Software Foundation
, which is a more idealistic, and stricter definition.
My perception, perhaps incomplete and/or errant, is that the open hardware community is less mature, and doesn't have people like Eric S. Raymond and Richard Stallman pushing for recognition of a set of stated principles. I'm sure there are people working in that direction, but perhaps not with the same level of visibility. Since Bruce Perens (instrumental in the Open Source world) has taken up hardware as a cause, perhaps this will change.
In re. whether some piece of hardware is truly "open", well, I doubt there will ever be complete consensus on that. In that aspect, I do agree with Draythomp that you take what's there in the spirit in which it was provided. This is the case in the world of Free and Open Source Software. For example, the GPL, BSD, and Apache licenses are all "open", but confer a differing set up usage licenses.