This one is difficult to answer. The Pi is very critical on it's power supply voltage.
Between 4.85 and 5.25V should be fine.
You need to calculate a small voltage drop on the cable, and a voltage drop over the polyfuse on the Pi board.
So, if a supply provides 5.1V, even under load, everything should be fine. If it's only 4.9V, things become tricky.
Both voltages however are fine to power a self powered usb hub. Also note that altough usb hub supplies are sometimes rated to be able to deliver 2 amps, they usually go on their knees at a much lower current delivery.
So, it's all a bit a hit or miss situation. I bought 3 1.2Amp 5V adapters. 2 work fine and one is giving a distortion in the picture. When I measure the output voltage, they are all 3 identical. I haven't measured the output ripple yet, but it's scary to see that even same brand and type isn't a guarantee for proper functioning on the pi.
I managed to get rid of the issue by changing a line in the config.txt to boost the hdmi signal, but this setting exists to compensate for hdmi cable losses, not to fix supply issues.
I do assume that powering the Pi from a free downstream port of the hub would fix the issues people are having with hubs that also provide power on their upstream port. When the hub adapter is plugged in, the pi should get it's full 5V, and should boot normally. No need to cut wires in the hub. So, if you need a hub, you might as well use it to power your Pi as well. All you need is the proper cable from usb to mini (micro) usb. Just try to find a good cable with thick power and ground wires, so that the voltage drop over the cable dosn't become 2 high. Measure the voltage on the Pi between TP1 and TP2 and see if it's between the limits mentionned before.
