RawTherapee is not set up to deal with RGB values outside the display range between 0.0f and 1.0f, neither for importing nor for exporting.
RawTherapee is not set up to allow the user to directly make mathematical operations on linear RGB, which is what I’m fairly sure you want to do, but maybe I misunderstand you.
RawTherapee is an awesomely excellent raw processor and has some amazing algorithms that allow for accomplishing various editing tasks. But I have a feeling it’s not the right software for the specific tasks that you have in mind.
For importing and exporting floating point images, you need an image editor that allows to import and export floating point tiffs or openexr images. One or both (depending on the software) can be imported and exported by Krita, GIMP 2.9, darktable, and PhotoFlow.
There’s a bunch of other software that also can be used to import/export floating point tiffs and/or openexr files. I only listed software that I use on a regular basis. @ggbutcher - can rawproc import and export floating point images?
There are some other file formats that can support or partially support RGB channel values outside the display range, but these other file formats are not as widely supported among various softwares as floating point tiffs and openexr images.
Please note that a “tonemapped” HDR image, though commonly referred to as “HDR”, is no longer an actual HDR image, precisely because it’s been tonemapped to fit in the display range (just as an interpolated raw file is no longer a raw file after it’s been interpolated and saved as some other format).