ONENGINEER - Regarding the potential conflict of interest on federally owned dams: That is a legitimate question.
USACE, Natural Resource Conservation Service, and Bureau of Reclamation generally do their own dam engineering. USACE engineering staff are mostly spread out among district offices, although they recently (5? years ago) started up a center of dam and levee expertise called the Risk Management Center. They provide some oversight and consistency among districts.
Reclamation's engineering staff that do dam safety studies are mostly concentrated in one office, which operates much like a captive consulting firm. Inspections for Reclamation dams are annual; complete reviews of design, performance, changes in the state of practice, etc. are done once every 6 years. Generally, there are two or more lines of internal review, including a board of finicky old men and women (generally PEs and PGs with 20-30 years experience), and for more complex problems, a board of outside hotdogs may be hired (names you would recognize - Ralph Peck and Harry Seed were among the favorites.) There is enough separation of engineering and dam-safety management that the process can become adversarial, but mostly that's good, because it forces everyone to have their technical arguments spelled out in detail for examination.
Smaller agencies are more likely to hire a consultant, or another federal agency with more engineering staff to act as a consultant.