I understand what you are trying to do, and maybe things have changed in the last few years, but I would not use own ( real or fake ) NS myself. It is just to tricky.
If your really want, maybe you can do a google search for whitelabel NS., or even better: How to setup your own nameservers so you get an understanding what is involved to setup real NS.
OVH is not forcing, I think it is normal to use the NS from the domainregistrar. I have a lot of domains at Namecheap, and also use their NS. Again : I understand why you want your own, but it is not as easy as 1 2 3 🙂