I agree with @SvenYargs in the comments:
Although the definition that better fits this context is probably (via Merriam-Webster):
the practice of relying on observation and experiment especially in the natural sciences
One can distinguish between theoretical and empirical sources for scientific evidence.
In this dichotomy, the theoretician is taking a more rationalist perspective (for an example of a paper taking this persepective see here), but I think it is inappropriate to expect to apply that pure dichotomy from epistemology to a typical practicing scientist. Instead, one should consider these as shared aspects of the philosophy of science rather than the philosophy of epistemology.
Rather, a theoretician is of the type that focuses on the theoretical approach; that doesn't mean they reject empirical evidence, but they may tend to be skeptical of evidence that is not grounded in theory (that is, one needs to be able to develop a predictive theory to interpret evidence in a meaningful way).
Similarly, used in context, an empiricist is not someone who thinks theoretical work is not "real" but rather they focus on empirical evidence in their work (that is, they may use theory to drive an experiment but the deciding factor is supportive experimental evidence).
For another example, Monaghan, F. V., & Corcos, A. F. (1985). Mendel, the empiricist. Journal of Heredity, 76(1), 49-54. use the theoretician/empiricist dichotomy to position the work of Gregor Mendel. Google scholar can suggest several other articles in which to find this dichotomy.
I would consider "experimentalist" to be a synonym, as well, which also fits well with the adjectives used for say, an experimental vs. theoretical physicist.