Is perspectivism a subtype of relativism?
Relativism in its naive form is that truth is merely relative, so perspectivism, which asserts that truth is relative to the perspective of the agent is one type of relativity of truth. Another type of relativity is social constructivism, which in a naive formulation asserts that truth is relative to the society of agents who collaborate to determine truth. Radical forms of relativism would deny that truth exists or that there is a means of determining truth. There are post-modernist extremists who argue this, but it's not a very popular philosophy even among post-modernist philosophers. In the analytic tradition, one dominant view is scientific realism, which believes that there is an external, observer-independent structured reality and that matters of truth reduce to empirical evidence based on observation. Philosophers of science in the 60's and 70's, however began taking stock of underdetermination of theory, theory ladenness, and social factors of scientific practice and essentially accepted that there is an essentially perspectivist basis for science and views on science. This is why WP's article on perspectivism asserts:
During the 21st century, perspectivism has led a number of developments within analytic philosophy and philosophy of science, particularly under the early influence of Ronald Giere, Jay Rosenberg, Ernest Sosa, and others. This contemporary form of perspectivism, also known as scientific perspectivism, is more narrowly focused than prior forms—centering on the perspectival limitations of scientific models, theories, observations, and focused interest, while remaining more compatible for example with Kantian philosophy and correspondence theories of truth.
Scientific realism is far more popular (according to PhilPapers) than instrumentalism, which is anti-realist in nature, but both positions presume that at the end of the day, despite the relativity of truth from the perspectives of various agents, theories, epistemologies, or societies, ultimately a consensus about objective, positivist reality is realizable in empirical methods. Daniel Dennett famously characterizes this as heterophenomenology which is a form of intersubjectivity. The quotation above mentions Kant, and implicit in that is the recognition that the phenomenological (subjective)/noumenological (objective) distinction is still fundamentally observed by contemporary philosophers.