No, you can't smoke the bark. Well, you can, but as someone else mentioned, you'd need to smoke a bunch all at once to get any effect. 2-5mg for a threshold? Maybe if what you want is a terribly weird body feeling and no visuals, 2-5mg would be fine. Maybe you're one of the lucky 1% who can have a full on deep space trip off tiny amounts. But maybe you're a part of the other 1% who will never have any effects from dmt. I know one of each from those populations.
Also, I'm pretty sure the dmt contained in MHRB is dmt-tannate. Don't know if that's even smokable. Just do an extraction yourself if you already have the mimosa root bark. Its simple, you can have pure, smokable, freebase dmt in under 24 hours.