I have a redtail in my 55g ... hard to put it in perspective, but he is the oldest fish in the tank (along with the yo-yos) and the largest.
My redtail takes great joy in chasing my yo-yo loaches around the tank. Doesn't typically interact with the cichlids, but I've seen him chase them also. My redtail, while showing his dominance has never hurt any of my fish (I've had him over 5 years).
My redtail does have a log decoration that is his. All the fish like to hide there as well, but I'm pretty sure he owns it.
I would recommend giving the redtail a hiding place.
Mine is kind of like a cat ... he comes out when he wants, does what he wants, and if so inclined chases the other fish. But typically, he's pretty mellow and just cruises around picking at the plants. I would say the times he actually chases the other fish is probably less that 5% of his time.
So, can he be aggressive, yes, but he doesn't nip fins or actually hurt the other fish. So, in my experience, I would downplay their aggressiveness.
Since I've had this shark so long, I've had him with guaramis, rainbows, tetras, mollies, etc. When I had those other fish he never once bothered them. 98% of the time he only ever chases the yo-yos and typically its the largest of the 3 (although they are all almost 4" now ... I've had the yo-yos for 5 years or so too). He's never bothered any of my plecos either.