The writing-mode attribute is ignored when rendering RadSvgImage.
Here is a sample SVG:
<svg width="200" height="200" viewBox="0 0 200 200" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:svg="http://www.w3.org/2000/svg">
<g>
<text style="font-size:20px;writing-mode:tb;" x="30" y="30">
Vertical text
</text>
<text style="font-size:20px;writing-mode:vertical-lr;" x="50" y="50">
Text 2
</text>
</g>
</svg>