Firstly, thank you for your patience.
After researching the case, it seems that the control has its internal logic for applying the styles of its elements. Thus, the Styles targeting the RadButton controls within it are not applied, as they are with lower priority. However, you can alter the default visual appearance through the usage of ItemContainerStyleSelector. This approach is demonstrated in the ToolBar Custom Styled Elements
SDK Example. The demo demonstrates applying a ToolTip as well. Can you please check it out?
Want to extend the target reach of your WPF applications, leveraging iOS, Android, and UWP? Try UI for Xamarin
, a suite of polished and feature-rich components for the Xamarin framework, which allow you to write beautiful native mobile apps using a single shared C# codebase.