It is surprising that not so many companies do as they do at MongoDB. Maybe because of the burden which needs to be taken to integrate a third-party tool for testing. Yes it costs resources but as MongoDB proofed - it pays off. I need to deal with many DBMSs. MongoDB has by far the least amount of patches - this in depth testing is surely one of the reason for this good result.
I like the mindset of reaching out to an external, unbiased resource to assist in continuous integration and improvement. The outside perspective helps to prevent confirmation bias in your internal testing processes and let's your users see an open, neutral, and transparent picture of your capabilities.