Travel insurance for Los Roques comes with a complication that matters more than any dive site or beach on the archipelago: Los Roques sits within Venezuela, and many governments currently advise against travel to Venezuela altogether, which changes what a policy can honestly promise you. Before anything else, check your own government's current advisory for Venezuela, since that status is what most insurers look at first.
The practical effect is significant. Many travel insurance policies contain a standard exclusion for trips to, or within, a country under a do-not-travel advisory, meaning claims arising during that trip - medical, cancellation, lost baggage, anything - can be declined regardless of what actually happens on the water. This is not unique to any one insurer; it is common wording across the industry, and it applies whether the incident happens on the mainland in Caracas or out on one of the cayes of Los Roques itself.
Access itself is part of the honest picture too. Los Roques has no bridge or ferry link from the mainland that most visitors use; the practical route is a short flight from Caracas's Maiquetia airport, and the archipelago's own facilities are minimal, with no real hospital on the cayes. Anything beyond minor first aid means transport back to the Venezuelan mainland, and from there, options depend heavily on conditions that can shift with little notice, which is exactly the kind of situation ordinary travel cover is designed for and exactly the kind an advisory-based exclusion can undermine.
If you are set on this trip, the honest step is to contact insurers directly, disclose Venezuela as the destination, and get the advisory exclusion confirmed in writing rather than assumed from general terms. Do not assume any policy covers travel a government currently advises against; check the policy wording specifically, and check whether your existing health cover extends abroad and to Venezuela at all before relying on it.