Did CrowdStrike have proof that Russia hacked the DNC?
Yes, and this is also supported by the U.S. Intelligence community and independent Congressional reports.
Following a comprehensive investigation that CrowdStrike detailed publicly, the company concluded in May 2016 that two separate Russian intelligence-affiliated adversaries breached the DNC network.
To reference, CrowdStrike's account of their DNC investigation, published on June 14, 2016, "CrowdStrike Services Inc., our Incident Response group, was called by the Democratic National Committee (DNC), the formal governing body for the US Democratic Party, to respond to a suspected breach. We deployed our IR team and technology and immediately identified two sophisticated adversaries on the network " COZY BEAR and FANCY BEAR ... . At DNC, COZY BEAR intrusion has been identified going back to summer of 2015, while FANCY BEAR separately breached the network in April 2016."
This conclusion has most recently been supported by the Senate Intelligence Committee in April 2020 issuing a report [intelligence.senate.gov] validating the previous conclusions of the Intelligence community, published on January 6, 2017, that Russia was behind the DNC data breach.
The Senate report states on page 48:
"The Committee found that specific intelligence as well as open source assessments support the assessment that President Putin approved and directed aspects of this influence campaign."
Furthermore, in his testimony in front of the House Intelligence Committee, Shawn Henry stated the following with regards to CrowdStrike's degree of confidence that the intrusion activity can be attributed to Russia, cited from page 24:
HENRY: We said that we had a high degree of confidence it was the Russian Government. And our analysts that looked at it and that had looked at these types of attacks before, many different types of attacks similar to this in different environments, certain tools that were used, certain methods by which they were moving in the environment,and looking at the types of data that was being targeted, that it was consistent with a nation-state adversary and associated with Russian intelligence.
Have any other organizations concluded that Russia was behind the DNC hack?
Yes. CrowdStrike's conclusion that Russia was behind the DNC hack is supported by the U.S. Intelligence community and also by independent Congressional reports. Most recently, the Senate Intelligence Committee released a report in April 2020 that validated the previous conclusions of the Intelligence Community Assessment, published on January 6, 2017, all concluding that Russia was behind the DNC data breach.