The short answer, is that, yes, a .NET developer can be helpful, if you design .NET SDK based agents.
ThingWorx itself allows you to use Javascript for your custom services, 99% of the time.
You can also use Java, in the form of ThingWorx Extensions in order to extend the platform with behavior that is not possible to achieve via Javascript - but, I want to reemphasize that Javascript is the main language that ThingWorx is offering to users like us to build applications. I'm saying this because I have seen users creating Java extensions that output pure HTML that was 100% achievable via Mashup Builder just because they were not familiar with ThingWorx Mashup Builder.
Depending on the developer, you might encounter people who can switch to Javascript (or other programming languages) relatively easily, but this is not always true.
Would it be possibly to share what is the context around your question (situation, what would you want to achieve, or the use-case)? In that case we would be able to help much better than guessing (like I did above). We do have specific trainings that we can recommend for new developers.
Another option is to also contact your PTC representative to discuss the situation in more detail, and then he/she can also recommend which trainings to go through.
