it's 0% to me... Yamato is 28, Rocks disbanded 38 years ago. BM said they havent met in decades so I'll assume that the last time they met was at the God Valley (Linlin was 30 yo, Kaido was an apprentice). Even if they met after that, I'd doubt they'd make kid bcs :
1. They clearly have a siblings-like relationship
2. Both have became enemies at that time
3. The debt thing. Now we know the debt he owed her is his fruit. So it's even more less likely, bcs some ppl thought Yamato was the debt he owed her.