For the newer miele warming drawer, the temp range is 104F-185F. So, 104F is their LOWEST setting. Since this is not really a cooking instrument, I will not put too much of my money on how accurate those temperature is, or how well it holds that temperature with time.

There are people who uses warming drawer to proof dough. It's even listed in the miele manual. For proofing dough, you should set it to the lowest setting (104F), and "allow the dough to proof for approx. 30mins or when it double its size"

My miele combi steam oven also has its own proofing program, which the default is set at 85F.

Basically, there is not a set temperature when it comes to proofing dough, and it varies depends on what kind of bread, and texture you want to achieve. Some dough are proof in the fridge (for a cold/delay/slow proof), some at room temp, but most bread for yeast dough are proof "ideally" at 85F-100F, that's when the yeast are most active.

so 104F is not too far off.

I hope that answers your question.