Madara was the person who collect the different clans that make up konoha by using his powers ,stated by itachi.This mean Madara did encounter an 8 gate user and knew method to counter him from their battle.
Where did he Itachi ever state that??? Seriously??? Because he united a few clans and then joined an organization based on already united clans does not mean, either.
1. "He collect the different clans that make up konoha"
nor
2. "Madara did encounter an 8 gate user and knew method to counter him from their battle."
also,
3. The panel you posted didnt prove either of your theories.
You DID prove that he contributed the diversity of Konoha when he joined the SENJU ORGANIZATION (Organization = collective of clans) but that still isnt proving that he had anything to do with any 8 gates user or that a clan of gate users even exists.
Cool reach, tho...