No. Determinism is not a scientific thesis.
Instead, it belongs to the philosophy of science. It helps to think of there being three levels. First, there is the world itself. Second, there are scientists studying the world, particularly its regularities. Third, there are philosophers of science who study the scientists who are studying the world.
For example, when a scientist notices regularity, he or she might propose a causal law. Causal laws have an "if -- then" form: if an event of this type occurs, then an event of that type occurs. If this happens, then that happens; alternatively, this causes that. Scientists attempt to fashion causal laws into comprehensive scientific theories. Therefore, scientists are trying to understand what causes what.
Notice that scientists take the notion of causation for granted. By way of contrast, philosophers of science do not. They wonder about what scientists are doing. For example, when a scientist claims that "If X, then Y" or "X causes Y", the philosopher of science may ask, "What is a cause?" The question "What is a cause?" is not itself a scientific question; scientists take for granted the notion of a cause. Philosophers of science do not. "What is a cause?" is a question in the philosophy of science. It is a philosophical question.
In other words, issues in the philosophy of science are more fundamental than issues in science. Whether or not determinism is true is one of those issues. Therefore, it's like the question about the nature of causation itself. This does not mean, though, that issues in the philosophy of science are more important than scientific issues. All it means is that they occur on a different level.