An IS auditor evaluating high-availability networks should be most concerned if:

In the context of evaluating high-availability networks, having servers clustered in one site raises significant concerns regarding potential points of failure. If an organization relies on clustered servers located at a single physical location, it risks exposure to various hazards that could disrupt service, such as natural disasters (e.g., earthquakes, floods), power outages, or man-made issues (e.g., fire, vandalism).

For high availability, it's crucial to distribute resources to mitigate risks tied to localized outages. By using multiple sites or employing geographically dispersed setups, organizations can ensure that if one cluster fails due to environmental conditions or other incidents, other operational components can continue to provide service. This redundancy is a cornerstone of high availability strategies.

In contrast, geographical dispersion, readiness of a hot site, and diverse routing are generally seen as positive measures for ensuring network resiliency. Geographically dispersed setups help in maintaining service continuity across different locations, while a hot site ensures that there is a rapid response capability in the event of a failure, and diverse routing aids in maintaining connectivity despite potential network interruptions. Thus, focusing solely on clusters in a single site highlights a significant vulnerability in the high-availability strategy.