Blueberries are self fertile. Cross pollination is helpful though.

Elliot is a very late variety while O'Neal starts early so I don't know if they help each other during pollination. Ozarkblue is a good pollinator with O'Neal. Anyway your two should give you a long bearing season.

well, with pollenizing between two different CATEGORIES (more than just different cultivars here, because Elliot is a Northern highbush, and O'Neal a Southern highbush...) seeming kind an intriguing, to-me-new or al least forgotten-about concept...
I just went and did a litle online searching...
and although little or nothing turned up about the general principle about northern and southern types of blueberries being able, or not, to pollenize each other ((did see one recommendation that, for pollenizing, southern highbush types be planted with other southern highbush types)...
"some" amount of info "did" surface about the blossoming times of Elliot blueberry and O Neal blueberry:

Elliot: very late blossoming

O'neal: long blossoming period

However, I'm not too sure these ratings are based on the same "scale"-- that is, are the blossoming times of NOrthern Types and Southern types comparable, or are they different?
One report I just noticed, mentioned that a third type, Rabbiteye blueberry, is on a different blossoming schedule in general, than Southern highbush blueberries (in general).

But what "really" caught my eye, was one detailed explanation of what might possibly be involved in O'neal blueberry being considered to have a "long" blossoming period: so long in extent, that O'neals commonly start blossoming "the previous FALL", often continuing on with more blossoming progress "during warm spells in winter" and then finishing up in spring. Talk about a "long" bloooming period!
Though probably additional specific information about the O'neal cultivar as to this question, is known by someone, who with luck maybe will come forward, ...at this point this ? (and some other stuff)is to me yet unclear ---whether or not O'neal blueberry bushes, would stand to have much of any not-yet-opened blossoms availble to open and spring, to help with pollenizing during the blossoming season of a late-blossoming cultivar like Elliot