I don’t know what GIMP’s built-in sRGB profile is or does so I can’t comment about that part. However, I can say a few words on RT’s profiles and on the general approach.
Which profile should you use when exporting from RawTherapee? Depends. RawTherapee makes precise color manipulation easy, while GIMP makes me feel like I’m knitting wearing motorcycle gloves. So I avoid doing any color work in GIMP and use it only to remove dust and scratches and such. If this is you, if you’re not using a wide-gamut monitor and if your final image is to be in sRGB, then export from RawTherapee using sRGB (RTv4_sRGB) and save yourself some hassle. Otherwise enter color management hell - here’s a sharp stick and a lighter, good luck.
If you’re exporting from RawTherapee using a color space larger than sRGB because you have a good need for doing so or because you hate yourself, then you should also be using a higher bit-depth format, e.g 16-bit TIFF or 16-bit PNG.
The color management page in RawPedia is not up to date - it is on my long TODO list.
Notice that RawTherapee now comes with an ICC profile creator, so if you need a profile we don’t ship you can easily generate your own, e.g. using ProPhoto primaries and a linear gamma.
As to the question of ICC v2 vs v4, there was a long debate between experts regarding this. No conclusion was reached, but no one was hurt either.