[rcxdude]

Short-term visas might be entirely appropriate for someone who's going to be working in the country for a short time to set something up. I've worked under one myself (You usually need to justify why someone already in the country couldn't do it, but "I designed the thing and literally no-one in your country has seen one before" tends to work). visa-waiver programs like the ESTA generally are not: they're mainly for tourism, conferences, and business/sales meetings, and the latter can get a little blurry depending on how much you are demoing something, but if you're doing actual work and you're being paid directly or indirectly by a US company you're probably not covered (which surprises a lot of people, and there's often stories of people getting kicked out of the country for relatively small pieces of 'work').

Either way, if these were actually workers in the country temporarily and in good faith to set up manufacturing, then it would neither seem to be a particularly good crackdown on illegal immigration nor encouraging manufacturing to be set up in the US.