In Mendix 8.4.1 I am adding SVG images as regular images within an ImageCollection.
Aside from this way of adding, it is going to be difficult. The functionality doesn't yet work in React Native out of the box.
What I have previously done is create a custom widget and use react-native-svg (https://github.com/react-native-community/react-native-svg)
Now comes a tricky part, width (at least) that Mendix version, you aren't using the latest React Native version and some manual steps are required (described on the Github page).
My best guess on lack of SVG support is that React Native doesn’t natively support SVG in its Image component. It looks like there are libraries that could add these capabilities: https://github.com/vault-development/react-native-svg-uri and https://github.com/react-native-community/react-native-svg
You could leverage one of these with a custom widget now, and I expect that we might see this capability built into the platform at some point in the future.