A kink does not necessarily mean another breed was added. Kinks, ranging from mild to severe, are fairly common in Am Stafs. In general, they are not shown or bred. But I do know of a couple that DID gain championships and were bred and produced many good dogs.I would say no. As a kinked tail indicates another breed was used somewhere in there. Also, it is not breed standard for any of the bull breeds, therefore would not be bettering the breed to reproduce.
Gemini is a cutie, but that is a pretty severe kink and he shouldn’t be bred, IMO.