Hello DreamVail, excellent question. The four bramaviharas, arise during non-dual practice. They are actually even more subtle, than what arises during the grosser jhanic states of absorption. The four bramaviharas are known as the immeasurables, because they can be cultivated without limit. Some might argue that they arise as inherent aspects of rigpa, our primordial awareness or buddha nature.

What I can tell you is that the bramaviharas ( metta, karuna, uppekha, and mudita ) arise for me when I do non-dual practice, such as mahamudra / dzogchen. They are natural and pure and arise from the absence of obscurations or delusional factors that have been either temporarily or permanently stilled. Non-dual practice does involve some element of concentration / samadhi / jhana.. so it would be misleading to state that there is no relation, however it is worth making a distinction between them and the typical jhanic factors. metta!