wpgraft never reads Oxygen’s data. There is no exporter, no importer and no shortcode translator anywhere in this, by design, because those are the parts that break. wpgraft reads the page as your browser rendered it: the real elements and the real computed styles on each one, at every breakpoint you ask for. It then rebuilds that as Beaver Builder’s own native elements, with the styles written into Beaver Builder’s own fields. Nothing that arrives depends on Oxygen still existing.
Both ends of this move are WordPress, which makes it the easy version of the job: the source page and the Beaver Builder editor can be two tabs of the same site, or two different sites on two different hosts, and it makes no difference, because nothing is exported and nothing has to match. You can leave the Oxygen page exactly where it is while you rebuild it, and compare the two side by side until you are happy.