Overall, multiboxing software tends simply reproduce your keystroke across multiple World of Warcraft clients. In that case, there generally isn’t anything wrong with it. It isn’t a supported playstyle, but neither is it prohibited.
If the program provides any kind of automation, even if you do not use it, that could cause an issue. If anything I’d recommend talking to the multiboxing community to see what their take on it is.
Sorry I couldn’t provide a clearer answer.