Yeah, it's easier to accept Amazing Man as part of the All-Star Squadron. That team never had stories in the 1940s, but there's nothing saying such a team couldn't have existed. However, I think it's a bit too easy to just have Will accepted by all these super-heroes and integrated into the team, when that wouldn't likely be the way it would have really gone down.
And it would have been a better story, if they had explored all the tensions in those times and if some super-heroes weren't as progressive as others. Given segregation, they could have really opened the door for a lot more diverse characters who simply weren't seen in the old comics, because they were not allowed onto those teams.
Like with the Seven Shadows in Chicago--see JSA 18 (January 2001)--there could have been other teams that we just never knew about in the 1940s. However, it's better to find representation where it exists in the actual comics, rather than making up stuff out of whole cloth. We should search for characters that are better candidates for representation than Alan Scott--there's just too much about the original Green Lantern that has to be retconned away.
There were actual persons of colour in the 1940s comics. Not so much in the mainstream comics, but in African-American owned newspapers that published comic strips about black characters. Maybe the publisher could work out a deal to license some of those characters for use. Bungleton Green would make a cool addition.