Heugel is a thing of itself, and some of its proponents get a bit long in the tooth about it. So short answer, just covering it in soil would not make a heugel mound.

However, it would make a really really amazing place to grow stuff! I have covered several wood piles and made gardens. The bug life is amazing! So many worms, so much other stuff, so much fungus.

Just make sure you don’t try to make a swale berm with wood. Wood floats. Then, your heugel turns into a raft and floats downhill and causes trouble. No joke! Heugel was originally a way to fill bogs and deal with Germany’s relatively bad soil, so it excels at making low areas high and high areas higher but more fertile.