The operation of the the hdbstabilizer is completely transparent, because it only undertakes operations on the blockchain. So if the current, well trusted operator (@smooth) ever decided to misuse those funds, it would quickly be detected and the proposal funding for it would be cut off extremely quickly.
Personally, having conversed with smooth for many years now, I have a high degree of confidence in his integrity, and I think this is true for many other stakeholders as well. But it's also worth pointing out that @smooth is one of the larger stakeholders in Hive, so it would not make much sense for him financially to abuse the funds he controls. And he's intentionally designed his bots to minimize the risks of malfeasance (for example, in the case the keys for the stabilizer-related accounts got hacked).
In summary, the risk for misuse of funds is very low, and the rewards from its operation are high.