No, it's not possible to export a splat map for the moment.
What you can do is creating masks in Instant Terra (mask from heights, mask from slope, erosion mask...), then you export these masks and use them in your favorite DCC to control the materials you apply on your terrain.
The feature is in our roadmap: you'll have the possibility to import a slap map (which will be called color map in Instant Terra) and apply it on a terrain. The splat map will follow the transformations you apply on the terrain (for the moment translation, rotation and scale, later also distorsion and other effects). Then you export the slap map. It will also be possible to convert a color ramp (AKA color gradient) to a splat map.
About our roadmap: we will make it public for the commercial release of Instant Terra (which will happen soon, stay tuned! ;-)).
Feel free to ask questions, we are happy to answer. :-)
Edit 2018: Export of color map (splat map) is now available in Instant Terra.