I was thinking the old E3b would come up but I don't think they are related to Cumans? Never heard of that can you elaborate?
The Cumans didn't passed to the Romanians autosomes,that's for sure,the anthropologic analysis is clear,no significant admixture took place;however, it is possible that some of the lords with this kind of ancestry passed the Y-DNA to some of their servants.
The Papal documents already spoke before the disaster from Kalka,that in the core of the Black Cumania(parts of the Moldavian and Eastern Wallachian plains),the Catholic Diocese with the seat in Milcov,the great majority are called Walati(Vlachs) of Greek rite,who had relentlessly opposed to conversion.
Most likely the Romanians and Cumans had very short-lived contacts(common military interest) and were very separated by the geography, the mountains vs. the plains,otherwise we would have seen a single, mixt,uniform, culture; in reality, the Cumans searched for the Bulgarian and Byzantine territories, after they were destroyed by the Mongols only few chieftains have remained to integrate into the Romanian society, many others have left ,also to Hungary.
The Romanians instead,although the Persian chronicle says that they were defeated too by the Mongols,still, by withdrawing into the mountains, they managed to survive,also as structures.
That's why the remaining Cuman leaders had no other option, but to embrace the Romanian identity, especially that they were probably used by the majority to make good treaties,including alliances, with the Mongols,since a lot of these have remained under the Hord authority, north of the Black Sea.
It would explain how Wallachia took a land from the Mongol suzerainty, the original land of Basarabia,if I recall the Horde had also sent some troops in support for Wallachia in the early 14th c.