Thank you for contacting us.
Indeed, the Text and Image primitives do not appear in the RadButtonElement's element tree in the Visual Style Builder tool. Due to the complexity of the issue, we will need a bit more time to investigate this case and provide you with proper answer. Please excuse us for the caused inconvenience. I will contact you back as soon as we have some results.
If you would like we can customize your theme. To do that please open a support ticket and attach the tssp file. Also, make sure that you describe the design you would like to achieve. Our team will perform the changes for you.
Thank you for your understanding.
All the best,
the Telerik team