Of course Binyamin Zev is two different names. It’s not like Aryeh Leib, which is a name and its Yiddish translation. It would be more like Yehuda Aryeh- a name of an animal, in this case, and the name of someone associated with it. But there is no reason why it should be separate names. If there is, I’d love to know.
Anyway, don’t Yiddish names ending in the “a” sound always end with an alef?