I was rewatching some episodes the other day and when the Jounins nominate the rookie 9 for the exam, they each state their full name. Asuma's full name is Sarutobi Asuma.

As far as Im aware they never mentioned who 3rds son / Konohamaru's dad was, and the Sarutobi (ala Sarutobi Sensei) part of Asumas name makes me think that maybe its him. There is a slight resemblance. The only problem though, is it seems like they would have mentioned Asuma being Hokages son at some point.