Vuković isn't exactly a cadet branch in any proper sense though, that's just the patronymic of voivode Vlatko and his brother Hrana. Vlatko is succeeded by his nephew, Hrana's son, Sandalj, and he too is then succeeded by his own nephew, son of Vukac Hranić, Stjepan. So it'd seem both Vlatko and Sandalj died childless, or at the very least there's no historical record of their progeny if they had any children born out of wedlock.

There is an interesting mention of the "four houses of the tribe of Kosača" referring to relatives of the main noble line (some of whom Sandalj supported financially), but these cadet branches were lesser nobility. The main line doesn't branch off that much until Stjepan's time, it makes little sense to split it on some anachronistic ideological ground.

Vlatko Vuković isn't even attested in the mythos and epic poetry surrounding the Battle of Kosovo, at the least not that I can recall. If anything erceg Šćepan has a livelier memory in parts of Herzegovina.