Do ultrasonic emitters work for spider, insect and/or rodent control? From all the sources I have read over the years, my opinion is, no, they do not. I have yet to come across an article from a reliable source that gives a resounding yes to this question.
Here is an article published by Kansas State University. It is quite long, so, I would skip to its conclusions and then go back through it if you want details.
Also, if you do a little research you will find that the FTC has fined and penalized companies for misleading the public with marketing information regarding these contraptions and the lack of scientific evidence to support the claims of what they can do.