Argb is a pwm signal. That's all that's necessary. 5v power can come from anywhere. And that's what a hub does. It provides upto 4.5A of Sata 5v to power the lights, the pwm signal just sets the address of each individual light and it's color.
So the header on the motherboard has only 1 job. Provide the pwm signal.
Given enough Sata plugs and a psu to push them, you can daisy chain upto 16x 6way hubs, or 72 fans worth of ARGB before running into pwm signal strength limits. All from a single JRainbow header.
ARGB and fan operation are 2 seperate things, 2 individual circuits, 5v and 12v. But ARGB itself is also the same, 2 individual circuits. 1 data and 1 power. They aren't combined anywhere except output to ground.
So as long as you can supply the correct voltage and sufficient amperage to the fan/strip, the only other concern is the signal from the header.
RGB is just the opposite. Where ARGB is a digital, front sided led, RGB is an analog back sided led. It gets power through all 3 filaments, ending in the 3 color wires which are grounds. Change the impedence on the ground wire and that changes the amperage through the filiment, changes the brightness of that filiment and its visible saturation.
If you think of ARGB as a pwm fan with its adaptability and limitations and a RGB as a 3pin DC fan with its limitations, you'd not be far off the truth.