Did Hop Harrigan ever work with the All-Star Squadron? Or the Justice Society? I've read the entire run of The All-Star Squadron, and I don't recall him ever appearing there. Can't say he never appeared in The Justice Society of America though.
Irritable Reptilian
Honestly, I'm just running off what the DC Wiki
says as far as Hop goes- I don't know the character at all. It may be one of the scenarios where the JSA (or some of its members) guest-starred in All-American Comics, rather than Hop coming across to theirs. Who knows?
And as far as leaving Batman out... eh. Honestly, it shouldn't make a huge difference either way- I've made it a bit of a point to show that Dick doesn't need the Batman connector; in most cases it simply shortens things.
Honestly, of all the ones done so far, the only one that I'm not sure can be done without Batman is Brother Power, the Geek. Swamp Thing can be reached through Adam Strange (not certain if Nightwing's met him, but Adam Strange has worked with Speedy/Arsenal, whom Dick knows well), or John Constantine (whom Dick has met at least briefly... I think in the nu52?), even if Dick hasn't met Swamp Thing personally, and all the others I've responded to have already been shown to be possible sans Batman.
Both Swamp Thing and Dick have met the Spectre, so there's that. And Superman, too (Superman met Swamp Thing at least twice).
This would probably be more fun if we left out Batman.