His neck is not a problem for me. He is after all an aged stallion.
With his score at the inspection , those of his foals, and his ability in the show ring I would consider breeding to him if I wanted a warmblood.
Now if he would cross well with an appendix mare is another issue. If she was more TB and not too lightly built then perhaps yes.
You might contact his owners and see if they are willing to approve your mare for breeding. You might want to get her approved in one of the warmblood or sporthorse registires.
Either way good luck. Shalom