Crashes from safety bugs are rare in HFT because they can replay years of data against code changes. For a strategy that trades in and out of positions quickly and is flat most of the time, it's also often not a big deal if the program crashes in the midst of running, as long as some technique has been arranged to cancel resting orders and alert a trader (who is generally monitoring the system's operations at all times).

They're certainly not inclined to pursue safety at any expense of performance in their code.