This is really a feature request. There is no answer other than that it currently does not.
Sideview is great stuff. Please use various tools they produce. Sideview makes a lot of high quality things that you can use or buy to use with Splunk.
In the last few years, the main focus has been on UI customization that does not require XML editing. I have no opinion on what the balance should be here, but you are asking about a different area than that focus.
Suggesting to add a higher quality XML editor to main Splunk is a good enhancement request which you should probably report via support. (I do not say this to waste your time. I say this because it's our current channel for reporting enhancement requests, and it's how customer interest is quantified.)
