Underarm hair can be harvested via FIT. I'm not sure, however, if the doctor has done very much of this. I think scalp, chest, stomach, back, and leg have more cases at the moment.
BHT can and has been performed via strip but not with Dr. Cole. Scalp strip is efficient in the sense that scalp has thick(er) hair at high density. This means a small strip can yield big numbers. Chest hair, for example, is usually not as thick or dense. The ratio of the amount of hair extracted to the size of the strip removed isn't favorable with body hair.
With scalp strip a single scar can be concealed with surrounding hair. Not so with body hair.
Now to your question about underarm strip. If a person did not have hair in this area it could cause irritation as this is a part of the body where skin rubs on skin. Hair is a "lubricant" of sorts. Yes, you could conceal this scar but FIT would be a better and less invasive choice.
The role of BHT is unfolding quickly in the world of hair restoration. Bht should be approached with FIT or FUE as these methods are better to the body and more efficient than strip.
Notice: I am not a doctor. My opinions are not necessarily those of Dr Cole. My advice is not medical advice.