From what I understand from your post one tag describes the actual output curves (for use by colormanaged applications), the other tag corrects the video output to match those described curves. I don't see where I get to control them though (aside from setting targets), I think it's done automatically...
My goal is to correct the non-colormanaged (as well as colormanaged obviously) output to the target white point.
VGA is an analog signal and because of this, an LCD must convert to digital signal before it can display the information. Therefore, you can theoretically adjust the analog signal prior to sampling for the digital signal. If the RGB buttons actually allow you to adjust the pre-amps, then they work akin to setting the correct white-balance prior to shooting JPG.
A good indication that the RGB buttons actually adjust the analog signal is when the RGB buttons are not available in DVI mode.
DVI is a digital signal, and the LCD could theoretically dump it straight to the panel. But a TFT panel doesn't have a normal gamma response, so the LCD has an internal lut to compensate for the difference. That way you can provide it with a relatively normal RGB signal and it will respond predictably.
Obviously, this then results in two places where the video signal is corrected. First in the video card (loaded from the special profile tag) and second in the LCD itself to make it "behave" normally.
This also means you can "calibrate" the device behavior in two places, provided of course that you can load the correction luts into the relevant locations.
So, if you have an LCD with a 14bit internal lut, a DDC connection, and compatible software, you can calibrate the internal lut so it behaves perfectly, and then you can simply leave the video card lut to a straight curve and not bother with the additional video card profile tags etc...
Displays and software that actually allow you to do this, won't leave you in the dark about the RGB buttons.
If you have an LCD with a 10bit or 12bit internal lut, and you have the RGB controls available in DVI mode, you could certainly use it. GMB match allows you to adjust the controls with measurement feedback. However, it usually doesn't do well with anything other than "native" white, because there usually is such a violent difference between pure white and shades of gray on LCD panels. This is where software like ColorEyes shines.
If you have an LCD with an 8to8bit lut, then it becomes a complete mist what to do with the controls. It may be that the LCD is using temporal dithering internally (because it is driving a 6bit panel for example) and therefore it may actually do something useful with the RGB controls. That's a lot of "mays" though, and in this case it is best to select the option with the least amount of tempering of the internal lut. (probably R=G=B=100 in user mode).
Given your goal to also have uncalibrated RGB displayed with a decent WB, you would want to calibrate to a single gamma curve for all three primaries. So, even if you choose "native" gamma, it should still be one and the same gamma value for all three primaries. I don't know whether your software allows you to control these settings, but software is the only place where you could influence this.