Duplicate: this is an exact duplicate "using controls from different vendors in one application", by the same author. Please do not answer it - answer the original question. Let's get this one closed as a duplicate.
Has anyone tried using controls from different vendors into your .NET application that uses winforms? Does this variety of controls go work together? Are there any problem so far?
Your question is very general, so I'll say generally speaking controls should have well-defined interfaces and should be interoperable. I have used controls from many sources together successfully.
If you are specifically talking about UI controls with a visual aspect, things get a bit more tricky, at least if you care about a consistent look-and-feel for your app. Many UI libraries allow you to skin the application (define a look once and apply it across the entire app). Unfortunately, they generally use different methods to achieve this goal. So if you combine UI components from different manufacturers, you might have quite a bit of work to get them to look good together if you depart from the standard OS look-and-feel.
If you are considering specific control libraries, post a more specific question.