I've found it suitable for rhinoceros beetles, but the results for rearing my stag beetles have varied wildly. I've had much larger and faster-growing larvae on mushroom cultures made with the same pellets and some wheat germ.
I tend to more frequently use my fermented substrate for rhinoceros beetles and as the substrate for getting females to lay eggs.
Here is Daniel Ambuehl's recipe for making flake soil from sawdust. No yeast or sugar, just bran and water with a small amount of existing beetle substrate as an inoculant. Just in case some of you have doubts concerning its efficacy, browse a few of his other videos to see some of the specimens he's produced using this exact formula.
I have tried both flour and yeast with sawdust and just frass with sawdust in the past. The frass and sawdust mixture took a little longer, but it did not stink nearly as badly.
I no longer keep rhinoceros beetles, so I've just been making edible mushroom cultures and using the mycelium-infested substrate directly or using it after it's spend and mushrooms are no longer produced for my stag beetles. No fermentation is required to produce rotten wood when the fungus breaks down the sawdust to produce white rot wood.