Are there any established treatments (I'm going to leave the exact terms a little bit vague because my understanding is vague) of which hobbies and interests are most likely to be attractive to someone with XYZ score on an OCEAN / Big 5 test?
TIA,
Yes. One example is that people high in Openness to New Experiences are interested in aesthetic experiences including museums and being in nature, and novel experiences as you'd expect from the name. https://psycnet.apa.org/record/1997-08808-031
Treatment is a bit misleading here to mean 'study', because in psychology it usually means 'intervention'.
Holland's RIASEC is probably the most studied such personality-based model of vocational choice. Note however that's not quite Big Five based though. See https://doi.org/10.1016/B978-0-12-804674-6.00025-9 for the details. It's way too much to get into the details here, but a teaser quote:
vocational interests are markedly more stable than the Big Five personality traits in adolescence and young adulthood (Low et al., 2005). Although the stability of both constructs increases during these life phases, the stability of interests becomes stronger, and vocational interests remain more stable than the Big Five personality traits for ages 22 to 29. From ages 30 to 39, the stability coefficients of the Big Five and vocational interests converge. However, even though vocational interests tend to be remarkably stable, there is still room for change.
[...]
The approach of viewing vocational interests as personality traits is based on personality models (e.g., the Neo-Socioanalytic Model of Personality; Roberts & Wood, 2006; McAdams & Pals, 2006) that distinguish between personality traits and motivations and consider interests and personality traits to be equivalent or regard interests explicitly as personality characteristics (e.g., Kandler, Zimmermann, & McAdams, 2014). By contrast, several other models of personality view interests as outcomes of personality traits (e.g., McCrae & Costa, 2008).
[...] Holland himself stated that vocational interests are “an important aspect of personality” (Holland, 1997, p. 8), and he defined the six interest types as “personality types” (Holland, 1997).
See also a review on the correlation of choice of academic major and Big Five personality (that's got some mainstream press coverage.)
Consistent findings across studies were that students of arts/humanities and psychology scored high on Neuroticism and Openness; students of political sc. scored high on Openness; students of economics, law, political sc., and medicine scored high on Extraversion; students of medicine, psychology, arts/humanities, and sciences scored high on Agreeableness; and students of arts/humanities scored low on Conscientiousness. [...] For all Big Five personality traits medium effect sizes were found frequently, and for Openness even large effect sizes were found regularly.
(Some will surely turn on the MBTI-style cliché/stereotype generator based on that.)
I'm not sure if there's that level of research depth for just "hobbies and [non-professional] interests" as opposed to vocational/academic-major choice, but probably there are some papers on the less professional interests. I'm not sure there's a unifying (attempt at) theory for just any interests, but one can surely find somewhat amusing/disparate papers like:
Collectors with an investment motive tend to have above-average education and financial means. High Openness and low Agreeableness significantly characterize their personality.