I don't think so, the sites seem to indicate free can also open dot files[0], I do believe there is a limit on the number of elements though.

IIRC I did some graphs for my bachelor thesis (10+ years ago) with graphviz, and then basically just passed them through OmniGraffle to make them beautiful.

[0] https://support.omnigroup.com/doc-assets//OmniGraffle-Mac/Om...