#4 Gangrel has appeared in AEW
Gangrel appeared for AEW during a cinematic match at the Full Gear pay-per-view in 2020. He appeared during the Elite Deletion match involving Matt Hardy and Sammy Guevara.
Gangrel returned chastising Matt Hardy for being disloyal to him during his days with the New Brood. The moment was out of the blue and was totally unexpected for AEW fans. It was recently reported that Gangeral was due to return again to AEW, but plans were nixed. They were put on-hold due to WWE's use of The Brood Gimmick for Edge on Friday Night SmackDown.
#3 Tommy Dreamer has appeared in AEW
Tommy Dreamer made a one-time appearance at the first-ever Double or Nothing pay-per-view in 2019. Dreamer was an entrant in the Casino Battle Royale. In fact, The Innovator of Violence eliminated fan favorite Orange Cassidy, making him an instant villain to the crowd. The two had come to blows trading low kicks.
Dreamer hasn't returned to All Elite since, and has resumed his career in IMPACT Wrestling. With the companies coming together time and again, it won't be a surprise to see Dreamer in an AEW ring again.