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Yes - in many cases my anubias does much better in substrate than tied to a rock or piece of driftwood. You should have no problems. Just be ready whenever the day comes that you want to move this plant, as you will pull up a wad of substrate half again as big as the plant.
I have the roots of my Anubias in gravel (i.e. not attached to any wood or rocks) and they do fine. They grow so well that I have to separate them to make room.
Even in regular substrate, my anubias has done fine. And when I had to pull up all the plants to redue the landscape, the roots were everywhere and at least 2 times the size of the plant.