I feel the split would hurt Rs more than Ds. Ds are more united generally but in many states that Harris would have a solid base in, AOC would be a non-factor (especially in the deep south) while Hawley and Haley split the R vote heavily. Here's a (very bad) rough map for a "best case 3rd parties" scenario
AOC Base: White liberals, progressive minorities
Harris Base: Minorities, establishment D types, some suburbanites
Haley Base: Suburbanites, establishment R types, some hispanic voting groups
Hawley Base: Rural white ultraconservatives, evangelicals