A heterogeneous swarm of marine robots was developed with the goal of autonomous long-term monitoring of environmental phenomena in the highly relevant ecosystem of Venice, Italy. As logistics are a continuing challenge in the field of marine robotics, especially when dealing with a large number of agents to be collected and redeployed per experimental run, an approach is needed that provides the benefits of simulation while also reflecting the complexity of the real world. This paper focuses on the development of a vehicle-in-the-loop test environment in which a surface station simulates and transmits the data of any number of simulated agents, while a real marine platform operates based on the received information. Several experimental runs of a specific use-case test scenario using the developed framework and carried out in the field are described and their results are examined.