My question: Can I simply
- look at the relevant DirectX 9 Microsoft .h files and add the
constants (rewriting of course not copy paste) from there?
I believe you can.
- do I have to do something more complicated?
No, I don't think so.
There are legal precedents if you like, e.g. the Microsoft/Lotus trial, but IANAL, so I don't think citing them would be much help. Reading publicly available header files and recreating them is what we've done, so you should be safe doing so as well. --Juan