There is also a conjecture that he has same mother as Nobuhide ODA (Obora) by association between their childhood names, but this is not likely because of following reasons: currently the leading hypothesis is that Nobuhide's birth mother is the Inaba clan, and also it is said that Nobuhide's birth mother became a concubine of Hideyoshi; If this theory is correct, there is no way to explain why Nobutaka was only allowed to call himself with the last name of Hashiba and his official court rank was Jugoige (Junior Fifth Rank, Lower Grade) Saemon no suke (assistant captain of the Left Division of Outer Palace Guards) and his territory was limited to 2000 koku compared to Nobuhide who promoted to daimyo with around 20000 to 50000 koku of chamberlains in addition to be allowed to call himself with the last name of Hashiba as a family member of Hideyoshi.
このほか、幼名との繋がりから織田信秀（大洞）と同腹との推測もあるが、信秀の生母は稲葉氏との推測が現在有力であり、また信秀生母は秀吉の側室となったと言われ、この説が正しいとすると信秀は秀吉の一族として羽柴姓を許されたほか侍従、2～5万石級の大名に昇進しているのに対して信高は羽柴姓を許されているのみで官位は従五位下佐衛門佐、所領も2000石どまりであることの説明がつかないことから、同腹である可能性は低いと思われる。