Is it safe? Almost certainly. Suppose it's 75% pure, you take 32mg of it, yielding an effective dose of 24mg, with 8mg of crap. Are any of the plausible impurities so nasty that consuming 8mg of them would be a problem? Doesn't really look like it... For 8mg to be a problem, your impurity would have to be pretty fucking toxic, 8mg is not much material...
Regardless, the cost per dose of quality 4-AcO-DMT is low, and everyone and their mom sells it, so why bother with this dirty crap? I would certainly choose not to take it, in light of the availability of clean stuff (which could be dosed more accurately as well), as a matter of principle.