They were aware of the effects of the charcoal and sawdust mixture. You are right, not really the paint was the secret.
And they never got anywhere with it because the war ended before it was ready. But it was very close.
By the time they build this, the Horten brothers had all the support they could get, but supplies were low and
time was short.
The 229 could outperform any other plane at that time.
They were not fully aware of what they had, since they could not fully develop it.
But they knew about it's flight capabilities after the first tests.
The RLMdid support the Hortens, but time and material was what they needed.

I believe they knew the plane's shape would leave a very low signature on the radar screen. But that is only my opinion, I can not prove it.

As a pilot, I am curious how the plane flew, flying wings are problematic, without a rudder they must have been
rather instable and hard to control.