Do you use a SIEM, log analyzer or any other Big Data solution for facilitating your risk assessments?

On my end for web apps, I'm using Acunetix and the good old reading logs and studying trends/patterns.

Of course the any logging collection/analysis facility would be of much benifit when conducting risk assessments.

Yes, IBM Qradar is equipped with QRM (Qradar Risk manager) which takes context from Vulnerabilities, create policy rules etc.