I actually asked this at the Biomedical center and they did not know what millet flour was.
I a little research online shows that the term “Millet” is very broad and refers to one or many types of grass grains. So you probably do not really know what type of millet is in the Millet Flour. In small amounts it should not be a problem, however there were some articles which mention using Millet flour as a replacement for regular flour could pose some nutritional and minor health risks.
I would probably try to avoid it if possible, and find a tortilla with something else in the ingredients.
Just my opinion though.