It depends on the fish and depends on the ph. Normally I would say that stability is more important than a specific parameter range and I would still stick to that. I don't think many are going to have a hard time adjusting to a close to neutral ph like 7.5.
However, you're talking about wild fish which do not always tolerate drastically changed conditions very well. I do think any should be fine in you water as far as ph goes, but depending on the species, you may need to provide incredibly consistent and clean water for them to thrive, sometimes this requires changing 100% or more of the aquarium water per day, with treated and seasoned water, which means it has been sitting long enough that the ph and other parameters are stable. PH out of the tap will usually change due to degassing and settling over the first 24 or so hours. "The Amazon" holds an incredibly vast diversity of life, and as far as species go, there's something like 50% of the species of fish on earth in that river. So it really depends on the fish you're looking to keep. Some specific amazonian fish such as wild discus, altum angelfish, cardinal tetras, do not tolerate anything but the cleanest and most stable water imaginable, otherwise they deteriorate or become sterile. For fish like these and many other sensitive ones, stability and the cleanest water possible is going to be the chore in trying to keep them. So, it's not ph you're going to have to worry about, but keeping up with water quality is going to be a near full time task depending on the fish.